Large Scale Magnetic Fields: Density Power Spectrum in Redshift Space
Indian Academy of Sciences (India)
Rajesh Gopal; Shiv K. Sethi
2003-09-01
We compute the density redshift-space power spectrum in the presence of tangled magnetic fields and compare it with existing observations. Our analysis shows that if these magnetic fields originated in the early universe then it is possible to construct models for which the shape of the power spectrum agrees with the large scale slope of the observed power spectrum. However requiring compatibility with observed CMBR anisotropies, the normalization of the power spectrum is too low for magnetic fields to have significant impact on the large scale structure at present. Magnetic fields of a more recent origin generically give density power spectrum ∝ 4 which doesn’t agree with the shape of the observed power spectrum at any scale. Magnetic fields generate curl modes of the velocity field which increase both the quadrupole and hexadecapole of the redshift space power spectrum. For curl modes, the hexadecapole dominates over quadrupole. So the presence of curl modes could be indicated by an anomalously large hexadecapole, which has not yet been computed from observation. It appears difficult to construct models in which tangled magnetic fields could have played a major role in shaping the large scale structure in the present epoch. However if they did, one of the best ways to infer their presence would be from the redshift space effects in the density power spectrum.
Matter density perturbation and power spectrum in running vacuum model
Geng, Chao-Qiang
2016-01-01
We investigate the matter density perturbation $\\delta_m$ and power spectrum $P(k)$ in the running vacuum model (RVM) with the cosmological constant being a function of the Hubble parameter, given by $\\Lambda = \\Lambda_0 + 6 \\sigma H H_0+ 3\
Power Spectrum Density of Stochastic Oscillating Accretion Disk
Indian Academy of Sciences (India)
G. B. Long; J. W. Ou; Y. G. Zheng
2016-06-01
In this paper, we employ a stochastic oscillating accretion disk model for the power spectral index and variability of BL Lac object S5 0716+714. In the model, we assume that there is a relativistic oscillation of thin accretion disks and it interacts with an external thermal bath through a friction force and a random force. We simulate the light curve and the power spectrum density (PSD) at (i) over-damped, (ii) critically damped and (iii) under-damped cases, respectively. Our results show that the simulated PSD curves depend on the intrinsic property of the accretion disk, and it could be produced in a wide interval ranging from 0.94 to 2.05 by changing the friction coefficient in a stochastic oscillating accretion disk model. We argue that accretion disk stochastic oscillating could be a possible interpretation for observed PSD variability.
Power Spectrum Density of Long-Term MAXI Data
Sugimoto, Juri; Mihara, Tatehiro; Sugizaki, Mutsumi; Serino, Motoko; Kitamoto, Shunji; Sato, Ryousuke; Ueda, Yoshihiro; Ueno, Shiro
Monitor of All-sky X-ray Image (MAXI) on the International Space Station has been observing the X-ray sky since 2009 August 15. It has accumulated the X-ray data for about four years, so far. X-ray objects are usually variable and their variability can be studied by the power spectrum density (PSD) of the X-ray light curves. We applied our method to calculate PSDs of several kinds of objects observed with MAXI. We obtained significant PSDs from 16 Seyfert galaxies. For blackhole binary Cygnus X-1 there was a difference in the shape of PSD between the hard state and the soft state. For high mass X-ray binaries, Cen X-3, SMC X-1, and LMC X-4, there were several peaks in the PSD corresponding to the orbital period and the superorbital period.
Power Spectrum Density of long-term MAXI data
Sugimoto, Juri; Sugizaki, Mutsumi; Serino, Motoko; Kitamoto, Shunji; Sato, Ryousuke; Ueda, Yoshihiro; Ueno, Shiro
2013-01-01
Monitor of All-sky X-ray Image (MAXI) on the International Space Station has been observing the X-ray sky since 2009 August 15. It has accumulated the X-ray data for about four years, so far. X-ray objects are usually variable and their variability can be studied by the power spectrum density (PSD) of the X-ray light curves.We applied our method to calculate PSDs of several kinds of objects observed with MAXI. We obtained significant PSDs from 16 Seyfert galaxies.For blackhole binary Cygnus X-1 there was a difference in the shape of PSD between the hard state and the soft state. For high mass X-ray binaries, Cen X-3, SMC X-1, and LMC X-4, there were several peaks in the PSD corresponding to the orbital period and the superorbital period.
Matter density perturbation and power spectrum in running vacuum model
Geng, Chao-Qiang; Lee, Chung-Chi
2016-10-01
We investigate the matter density perturbation δm and power spectrum P(k) in the running vacuum model (RVM) with the cosmological constant being a function of the Hubble parameter, given by Λ = Λ0 + 6σHH0 + 3νH2, in which the linear and quadratic terms of H would originate from the QCD vacuum condensation and cosmological renormalization group, respectively. Taking the dark energy perturbation into consideration, we derive the evolution equation for δm and find a specific scale dcr = 2π/kcr, which divides the evolution of the universe into the sub and super-interaction regimes, corresponding to k ≪ kcr and k ≫ kcr, respectively. For the former, the evolution of δm has the same behavior as that in the ΛCDM model, while for the latter, the growth of δm is frozen (greatly enhanced) when ν + σ > ( matter and dark energy. It is clear that the observational data rule out the cases with ν < 0 and ν + σ < 0, while the allowed window for the model parameters is extremely narrow with ν , |σ | ≲ {O}(10^{-7}).
Matter density perturbation and power spectrum in running vacuum model
Geng, Chao-Qiang; Lee, Chung-Chi
2017-01-01
We investigate the matter density perturbation δm and power spectrum P(k) in the running vacuum model, with the cosmological constant being a function of the Hubble parameter, given by Λ = Λ0 + 6σHH0 + 3νH2, in which the linear and quadratic terms of H would originate from the QCD vacuum condensation and cosmological renormalization group, respectively. Taking the dark energy perturbation into consideration, we derive the evolution equation for δm and find a specific scale dcr = 2π/kcr, which divides the evolution of the universe into the sub-interaction and super-interaction regimes, corresponding to k ≪ kcr and k ≫ kcr, respectively. For the former, the evolution of δm has the same behaviour as that in the Λ cold dark model, while for the latter, the growth of δm is frozen (greatly enhanced) when ν + σ > (extremely narrow with ν , |σ | ≲ O(10^{-7}).
Analysing MUAP of EMG Signal with Power Density Spectrum in Matlab
Directory of Open Access Journals (Sweden)
Akash Kumar Bhoi
2013-07-01
Full Text Available The lack of a proper description of the EMG signal is probably the greatest single factor which has hampered the development of electromyography into a precise discipline. Our proposed methodology described the relationship between the EMG signal and the properties of a contracting muscle by analysing its power density spectrum. We have also discussed the basic concepts on Motor Unit Action potential and analyzed the spectral density of a healthy person EMG signal. The Power spectral Density is calculated with Welch's PSD estimate method by taking Hamming {&} Kaiser Window. This model can be useful for the study of gate analysis and control scheme of the peripheral nervous system
The \\HI column density power spectrum of six nearby spiral galaxies
Dutta, Prasun
2013-01-01
We propose a method to determine the power spectrum of \\HI column density fluctuations using radio-interferometric observations of 21-cm emission from the ISM of galaxies. We have used this to estimate the power spectra of six nearly face on nearby spiral galaxies. Earlier work has shown that these power spectra are well fitted by power laws with slopes around -1.6 across length-scales $\\sim 1 \\, {\\rm kpc}$ to $\\sim 10 \\, {\\rm kpc}$, the amplitude however was undetermined. In the present work we have determined the amplitude of the \\HI column density power spectrum. We find that the \\HI column density $N_{\\rm HI}$ expressed in units of $10^{20} \\, {\\rm cm}^{-2}$ has mean square fluctuations in the range $\\sim 0.03$ to $\\sim 20$. The amplitude of the power spectrum is found to be tightly correlated with the \\HI mass fraction of the galaxies. The physical process responsible for these scale-invariant fluctuations is, however, at present not known.
Bartelmann, Matthias; Kozlikin, Elena; Lilow, Robert; Dombrowski, Johannes; Mildenberger, Julius
2016-01-01
In earlier work, we have developed a Kinetic Field Theory (KFT) for cosmological structure formation and showed that the non-linear density-fluctuation power spectrum known from numerical simulations can be reproduced quite well even if particle interactions are taken into account to first order only. Besides approximating gravitational interactions, we had to truncate the initial correlation hierarchy of particle momenta at the second order. Here, we substantially simplify KFT. We show that its central object, the free generating functional, can be factorized, taking the full hierarchy of momentum correlations into account. The factors appearing in the generating functional have a universal form and can thus be tabulated for fast access in perturbation schemes. Our results show that the complete hierarchy of initial momentum correlations is responsible for a characteristic deformation in the density-fluctuation power spectrum, caused by mode transport independent of the particle interaction. At the present e...
Cosmological Density and Power Spectrum from Peculiar Velocities Nonlinear Corrections and PCA
Silberman, L; Eldar, A; Zehavi, I
2001-01-01
we allow for nonlinear effects in the likelihood analysis of galaxy peculiar velocities, and obtain ~35%-lower values for the cosmological density parameter and for the amplitude of mass-density fluctuations. The power spectrum in the linear regime is assumed to be a flat LCDM model (h=0.65, n=1, COBE) with only Om_m as a free parameter. Since the likelihood is driven by the nonlinear regime, we "break" the power spectrum at k_b=0.2 h/Mpc and fit a power law at k>k_b. This allows for independent matching of the nonlinear behavior and an unbiased fit in the linear regime. The analysis assumes Gaussian fluctuations and errors, and a linear relation between velocity and density. Tests using mock catalogs that properly simulate nonlinear effects demonstrate that this procedure results in a reduced bias and a better fit. We find for the Mark3 and SFI data Om_m=0.32+-0.06 and 0.37+-0.09 respectively, with sigma_8*Om_m^0.6 =0.49+-0.06 and 0.63+-0.08, in agreement with constraints from other data. The quoted 90% erro...
Gas Density Fluctuations in the Perseus Cluster: Clumping Factor and Velocity Power Spectrum
Zhuravleva, I; Arevalo, P; Schekochihin, A A; Allen, S W; Fabian, A C; Forman, W R; Sanders, J S; Simionescu, A; Sunyaev, R; Vikhlinin, A; Werner, N
2015-01-01
X-ray surface brightness fluctuations in the core of the Perseus Cluster are analyzed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 8 to 12 per cent on scales of ~10-30 kpc within radii of 30-160 kpc from the cluster center and from 9 to 7 per cent on scales of ~20-30 kpc in an outer, 60-220 kpc annulus. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90-140 km/s on ~20-30 kpc scales and 70-100 km/s on smaller scales ~7-10 kpc. The velocity power spectrum is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the power spectrum of the density fluctuations is low...
Gas density fluctuations in the Perseus Cluster: clumping factor and velocity power spectrum
Energy Technology Data Exchange (ETDEWEB)
Zhuravleva, I.; Churazov, E.; Arevalo, P.; Schekochihin, A. A.; Allen, S. W.; Fabian, A. C.; Forman, W. R.; Sanders, J. S.; Simionescu, A.; Sunyaev, R.; Vikhlinin, A.; Werner, N.
2015-05-20
X-ray surface brightness fluctuations in the core of the Perseus Cluster are analysed, using deep observations with the Chandra observatory. The amplitude of gas density fluctuations on different scales is measured in a set of radial annuli. It varies from 7 to 12 per cent on scales of ~10–30 kpc within radii of 30–220 kpc from the cluster centre. Using a statistical linear relation between the observed amplitude of density fluctuations and predicted velocity, the characteristic velocity of gas motions on each scale is calculated. The typical amplitudes of the velocity outside the central 30 kpc region are 90–140 km s^{-1} on ~20–30 kpc scales and 70–100 km s^{-1} on smaller scales ~7–10 kpc. The velocity power spectrum (PS) is consistent with cascade of turbulence and its slope is in a broad agreement with the slope for canonical Kolmogorov turbulence. The gas clumping factor estimated from the PS of the density fluctuations is lower than 7–8 per cent for radii ~30–220 kpc from the centre, leading to a density bias of less than 3–4 per cent in the cluster core. Uncertainties of the analysis are examined and discussed. Future measurements of the gas velocities with the Astro-H, Athena and Smart-X observatories will directly measure the gas density–velocity perturbation relation and further reduce systematic uncertainties in this analysis.
Rapid modelling of the redshift-space power spectrum multipoles for a masked density field
Wilson, M. J.; Peacock, J. A.; Taylor, A. N.; de la Torre, S.
2017-01-01
In this work, we reformulate the forward modelling of the redshift-space power spectrum multipole moments for a masked density field, as encountered in galaxy redshift surveys. Exploiting the symmetries of the redshift-space correlation function, we provide a masked-field generalization of the Hankel transform relation between the multipole moments in real and Fourier space. Using this result, we detail how a likelihood analysis requiring computation for a broad range of desired P(k) models may be executed 103-104 times faster than with other common approaches, together with significant gains in spectral resolution. We present a concrete application to the complex angular geometry of the VIMOS Public Extragalactic Redshift Survey PDR-1 release and discuss the validity of this technique for finite-angle surveys.
Institute of Scientific and Technical Information of China (English)
WANG Zheng; ZHU Dianxiang
2007-01-01
This paper took the upper-lower wide belt sander B229 with four-feet wide belts,manufactured in China,as the study target.By means of framework dynamic design,we study its vibration characteristics by commencing from the place having horizontal defects and used experimental modal analysis (EMA) and power spectrum density (PSD) to observe the sanding parts and the whole machine,respectively.In the modal test,we mainly adopted the cross spots testing method to get the frequency response function of the fixed spots to every excitation vibration spot,then applied the SISO frequency response function and the frequency response function fitting method to identify and complete parameter recognition,respectively.The typical frequency response function chart of the whole machine and its sanding parts,as well as its second-order mode charts of contacting roller,were obtained.Through PSD analysis,we can get the amplitude-frequency spectrum and drive frequency.
Correlation between peak energy and Fourier power density spectrum slope in gamma-ray bursts
Dichiara, S; Amati, L; Frontera, F; Margutti, R
2016-01-01
The origin of the gamma-ray burst (GRB) prompt emission still defies explanation, in spite of recent progress made, for example, on the occasional presence of a thermal component in the spectrum along with the ubiquitous non-thermal component that is modelled with a Band function. The combination of finite duration and aperiodic modulations make GRBs hard to characterise temporally. Although correlations between GRB luminosity and spectral hardness on one side and time variability on the other side have long been known, the loose and often arbitrary definition of the latter makes the interpretation uncertain. We characterise the temporal variability in an objective way and search for a connection with rest-frame spectral properties for a number of well-observed GRBs. We studied the individual power density spectra (PDS) of 123 long gamma-ray bursts with measured redshift, rest-frame peak energy Ep,i of the time-averaged nuFnu spectrum, and well-constrained PDS slope alpha detected with Swift, Fermi and past s...
Early Structure Formation from Primordial Density Fluctuations with a Blue, Tilted Power Spectrum
Hirano, Shingo; Zhu, Nick; Yoshida, Naoki; Spergel, David; Yorke, Harold W.
2015-11-01
While observations of large-scale structure and the cosmic microwave background (CMB) provide strong constraints on the amplitude of the primordial power spectrum (PPS) on scales larger than 10 Mpc, the amplitude of the power spectrum on sub-galactic length scales is much more poorly constrained. We study early structure formation in a cosmological model with a blue-tilted PPS. We assume that the standard scale-invariant PPS is modified at small length scales as P(k)∼ {k}{m{{s}}} with ms > 1. We run a series of cosmological hydrodynamic simulations to examine the dependence of the formation epoch and the characteristic mass of primordial stars on the tilt of the PPS. In models with ms > 1, star-forming gas clouds are formed at z > 100 when the formation of hydrogen molecules is inefficient because the intense CMB radiation destroys chemical intermediates. Without efficient coolant, the gas clouds gravitationally contract while retaining a high temperature. The protostars formed in such “hot” clouds grow very rapidly through accretion to become extremely massive stars that may leave massive black holes with a few hundred solar masses at z > 100. The shape of the PPS critically affects the properties and the formation epoch of the first generation of stars. Future experiments on CMB polarization and spectrum distortion may provide important information on the nature of the first stars and their formation epoch, and hence on the shape of the small-scale power spectrum.
Dunn, H. J.
1981-01-01
A computer program for performing frequency analysis of time history data is presented. The program uses circular convolution and the fast Fourier transform to calculate power density spectrum (PDS) of time history data. The program interfaces with the advanced continuous simulation language (ACSL) so that a frequency analysis may be performed on ACSL generated simulation variables. An example of the calculation of the PDS of a Van de Pol oscillator is presented.
Early structure formation from primordial density fluctuations with a blue-tilted power spectrum
Hirano, Shingo; Yoshida, Naoki; Spergel, David; Yorke, Harold W
2015-01-01
While observations of large-scale structure and the cosmic microwave background (CMB) provide strong constraints on the amplitude of the primordial power spectrum (PPS) on scales larger than 10 Mpc, the amplitude of the power spectrum on sub-galactic length scales is much more poorly constrained. We study early structure formation in a cosmological model with a blue-tilted PPS. We assume that the standard scale-invariant PPS is modified at small length scales as $P(k) \\sim k^{m_{\\rm s}}$ with $m_{\\rm s} > 1$. We run a series of cosmological hydrodynamic simulations to examine the dependence of the formation epoch and the characteristic mass of primordial stars on the tilt of the PPS. In models with $m_{\\rm s} > 1$, star-forming gas clouds are formed at $z > 100$, when formation of hydrogen molecules is inefficient because the intense CMB radiation destroys chemical intermediates. Without efficient coolant, the gas clouds gravitationally contract while keeping a high temperature. The protostars formed in such ...
Exact third-order density perturbation and one-loop power spectrum in general dark energy models
Directory of Open Access Journals (Sweden)
Seokcheon Lee
2014-09-01
Full Text Available Under the standard perturbation theory (SPT, we obtain the fully consistent third-order density fluctuation and kernels for the general dark energy models without using the Einstein–de Sitter (EdS universe assumption for the first time. We also show that even though the temporal and spatial components of the SPT solutions cannot be separable, one can find the exact solutions to any order in general dark energy models. With these exact solutions, we obtain the less than % error correction of one-loop matter power spectrum compared to that obtained from the EdS assumption for k=0.1 hMpc−1 mode at z=0(1,1.5. Thus, the EdS assumption works very well at this scale. However, if one considers the correction for P13, the error is about 6 (9, 11% for the same mode at z=0(1,1.5. One absorbs P13 into the linear power spectrum in the renormalized perturbation theory (RPT and thus one should use the exact solution instead of the approximation one. The error on the resummed propagator N of RPT is about 14 (8, 6% at z=0(1,1.5 for k=0.4 hMpc−1. For k=1 hMpc−1, the error correction of the total matter power spectrum is about 3.6 (4.6, 4.5% at z=0(1,1.5. Upcoming observation is required to archive the sub-percent accuracy to provide the strong constraint on the dark energy and this consistent solution is prerequisite for the model comparison.
Exact Third-Order Density Perturbation and One-Loop Power Spectrum in General Dark Energy Models
Lee, Seokcheon; Biern, Sang Gyu
2014-01-01
Under the standard perturbation theory (SPT), we obtain the fully consistent third-order density fluctuation and kernels for the general dark energy models without using the Einstein-de Sitter (EdS) universe assumption for the first time. We also show that even though the temporal and spatial components of the SPT solutions can not be separable, one can find the exact solutions to any order in general dark energy models. With these exact solutions, we obtain the less than \\% error correction of one-loop matter power spectrum compared to that obtained from the EdS assumption for $k = 0.1 {\\rm h\\, Mpc}^{-1}$ mode at $z = 0$ (1, 1.5). Thus, the EdS assumption works very well at this scale. However, if one considers the correction for $P_{13}$, the error is about 6 (9, 11) \\% for the same mode at $z = 0$ (1, 1.5). One absorbs $P_{13}$ into the linear power spectrum in the renormalized perturbation theory (RPT) and thus one should use the exact solution instead of the approximation one. The error on the resummed p...
Afdala, Adfal; Nuryani, Nuryani; Satrio Nugroho, Anto
2017-01-01
Atrial fibrillation (AF) is a disorder of the heart with fairly high mortality in adults. AF is a common heart arrythmia which is characterized by a missing or irregular contraction of atria. Therefore, finding a method to detect atrial fibrillation is necessary. In this article a system to detect atrial fibrillation has been proposed. Detection system utilized backpropagation artifical neural network. Data input in this method includes power spectrum density of R-peaks interval of electrocardiogram which is selected by wrapping method. This research uses parameter learning rate, momentum, epoch and hidden layer. System produces good performance with accuracy, sensitivity, and specificity of 83.55%, 86.72 % and 81.47 %, respectively.
Guidorzi, C; Amati, L; Campana, S; Orlandini, M; Romano, P; Stamatikos, M; Tagliaferri, G
2012-01-01
We calculate the average power density spectra (PDS) of 244 long gamma-ray bursts detected with the Swift Burst Alert Telescope in the 15-150 keV band from January 2005 to August 2011. For the first time we derived the average PDS in the source rest frame of 97 GRBs with known redshift. For 49 of them an average PDS was also obtained in a common source-frame energy band to account for the dependence of time profiles on energy. Previous results obtained on BATSE GRBs with unknown redshift showed that the average spectrum in the 25-2000 keV band could be modelled with a power-law with a 5/3 index over nearly two decades of frequency with a break at ~1 Hz. Depending on the normalisation and on the subset of GRBs considered, our results show analogous to steeper slopes (between 1.7 and 2.0) of the power-law. However, no clear evidence for the break at ~1 Hz was found, although the softer energy band of BAT compared with BATSE might account for that. We instead find a break at lower frequency corresponding to a ty...
Characteristics of power spectrum density function of EMG during muscle contraction below 30%MVC.
Roman-Liu, Danuta; Konarska, Maria
2009-10-01
The aim of the study was to quantify changes in PSDF frequency bands of the EMG signal and EMG parameters such as MF, MPF and zero crossing, with an increase in the level of muscle contractions in the range from 0.5% to 30% RMS(max) and to determine the frequency bands with the lowest dependency on RMS level so that this could be used in investigating muscle fatigue. Sixteen men, aged from 23 to 33 years old (mean 26.1), who participated in the study performed two force exertion tests. Fragments of EMG which corresponded to the levels of muscle contraction of 0.5%, 1%, 2.5%, 5%, 10%, 15%, 20%, 25%, 30% RMS(max) registered from left and right trapezius pars descendents (TP) and left and right extensor digitorum superficialis (ED) muscles were selected for analysis. The analysis included changes in standard parameters of the EMG signal and changes in PSDF frequency bands, which occurred across muscle contraction levels. To analyze changes in PSDF across the level of muscle contraction, the spectrum was divided into six frequency bandwidths. The analysis of parameters focused on the differences in those parameters between the analyzed muscles, at different levels of muscle contraction. The study revealed that, at muscle contraction levels below 5% RMSmax, contraction level influences standard parameters of the EMG signal and that at such levels of muscle contraction every change in muscle contraction level (recruitment of additional MUs) is reflected in PSDF. The frequency band with the lowest dependency on contraction level was 76-140 Hz for which in both muscles no contraction level effect was detected for contraction levels above 5% RMS(max). The reproducibility of the results was very high, since the observations in of the left and right muscles were almost equal. The other factor, which strongly influences PSDF of the EMG signal, is probably the examined muscle structure (muscle morphology, size, function, subcutaneous layer, cross talk). It seems that low
Correa, Camila A; Schaye, Joop; Duffy, Alan R
2015-01-01
We explore the relation between the structure and mass accretion histories of dark matter halos using a suite of cosmological simulations. We confirm that the formation time, defined as the time when the virial mass of the main progenitor equals the mass enclosed within the scale radius, correlates strongly with concentration. We provide a semi-analytic model for halo mass history that combines analytic relations with fits to simulations. This model has the functional form, $M(z) = M_{0}(1+z)^{\\alpha}e^{\\beta z}$, where the parameters $\\alpha$ and $\\beta$ are directly correlated with concentration. We then combine this model for the halo mass history with the analytic relations between $\\alpha$, $\\beta$ and the linear power spectrum derived by Correa et al. (2014) to establish the physical link between halo concentration and the initial density perturbation field. Finally, we provide fitting formulas for the halo mass history as well as numerical routines, we derive the accretion rate as a function of halo ma...
Supernovae anisotropy power spectrum
Ghodsi, Hoda; Habibi, Farhang
2016-01-01
We contribute another anisotropy study to this field of research using Supernovae Type Ia (SNe Ia). In this work, we utilise the power spectrum calculation method and apply it to both the current SNe Ia data and simulation. Our simulations are constructed with the characteristics of the upcoming survey of the Large Synoptic Survey Telescope (LSST), which shall bring us the largest SNe Ia collection to date. We make predictions for the amplitude of a possible dipole anisotropy or anisotropy in higher multipole moments that would be detectable by the LSST.
Density Spectrums from Kinetic Inflations
Hwang, J
1996-01-01
The pole-like accelerated expansion stages purely driven by the coupling between the gravity and the dilaton field without referring to the potential term can be realized in a class of generalized gravity theories. We consider three such scenarios based on the scalar-tensor gravity, the induced gravity and the string theory. Quantum fluctuations during the expansion stages (including more general situations) can be derived in exact analytic forms. Assuming that the pole-like acceleration stage provides a viable inflation scenario in the early universe we derive the generated classical density spectrums. The generated classical density field shows a generic tilted spectrum with $n \\simeq 4$ which differs from the observed spectrum supporting $n \\simeq 1$.
Modelling the TSZ power spectrum
Energy Technology Data Exchange (ETDEWEB)
Bhattacharya, Suman [Los Alamos National Laboratory; Shaw, Laurie D [YALE; Nagai, Daisuke [YALE
2010-01-01
The structure formation in university is a hierarchical process. As universe evolves, tiny density fluctuations that existed in the early universe grows under gravitational instability to form massive large scale structures. The galaxy clusters are the massive viralized objects that forms by accreting smaller clumps of mass until they collapse under their self-gravity. As such galaxy clusters are the youngest objects in the universe which makes their abundance as a function of mass and redshift, very sensitive to dark energy. Galaxy clusters can be detected by measuring the richness in optical waveband, by measuring the X-ray flux, and in the microwave sky using Sunyaev-Zel'dovich (SZ) effect. The Sunyaev-Zel'dovich (SZ) effect has long been recognized as a powerful tool for detecting clusters and probing the physics of the intra-cluster medium. Ongoing and future experiments like Atacama Cosmology Telescope, the South Pole Telescope and Planck survey are currently surveying the microwave sky to develop large catalogs of galaxy clusters that are uniformly selected by the SZ flux. However one major systematic uncertainties that cluster abundance is prone to is the connection between the cluster mass and the SZ flux. As shown by several simulation studies, the scatter and bias in the SZ flux-mass relation can be a potential source of systematic error to using clusters as a cosmology probe. In this study they take a semi-analytic approach for modeling the intra-cluster medium in order to predict the tSZ power spectrum. The advantage of this approach is, being analytic, one can vary the parameters describing gas physics and cosmology simultaneously. The model can be calibrated against X-ray observations of massive, low-z clusters, and using the SZ power spectrum which is sourced by high-z lower mass galaxy groups. This approach allows us to include the uncertainty in gas physics, as dictated by the current observational uncertainties, while measuring the
Hashimoto, Y.; Shimizu, C.; Kishi, S.; Chao, Y. E.; Wan-Chung, L.
2016-12-01
Changes in stress state with seismic cycles are significant to understand the magnitude and nature of earthquakes. 1999 Chi-Chi earthquake occurred along the Chelung-pu fault, Taiwan. Structural data was obtained from core samples from Taiwan Chelung-pu fault Drilling Project (TCDP). Paleo-stress analysis revealed that the paleo-stress changes between horizontal compression and horizontal extension, which possibly corresponds to stress change before and after earthquake (Hashimoto et al., 2015). The microfault inversion analysis provided an opportunity to classify the micro-faults corresponding to the stress state before and after earthquake. In this study, we have analyzed roughness of micro-faults using power spectrum density and Hurst exponent to understand the roughness change with seismic cycles. Micro-faults were classified into two groups related to stress state before and after earthquake using misfit angle. Misfit angle is the angle between calculated slip direction and observed slip direction for each estimated stress state. Microfaults were sampled from TCDP core. 12 of each samples for horizontal compression and horizontal extension stress state were analyzed. 3D surface data of the slip surface of microfaults were obtained by 3D macro scope (Keyence, VR-3200). Three lines in a surface were analyzed to get power spectrum density-wave number relationships. Hurst exponent is a parameter related to a slope of a log-linear decreasing line in power spectrum density-wave number relationship. Power spectrum density before earthquake is smaller than that after earthquake. Hurst exponent is constant around 0.73-0.75 both in the stress states before and after earthquake. The differences between the directions parallel or vertical to the slip direction were not observed. These results suggest that amplitude decreases with slip at the time of horizontal compression (stress state before earthquake) at to keep the slope in power spectrum density-wave number
Perumal, Praveen; Anitha, Kuttae Viswanathan; Reddy, Jetti Ramesh; Muthukumar, Balasubramanium
2016-01-01
PURPOSE This pilot study was to find the influence of complete denture on the brain activity and cognitive function of edentulous patients measured through Electroencephalogram (EEG) signals. MATERIALS AND METHODS The study recruited 20 patients aged from 50 to 60 years requiring complete dentures with inclusion and exclusion criteria. The brain function and cognitive function were analyzed with a mental state questionnaire and a 15-minute analysis of power spectral density of EEG alpha waves. The analysis included edentulous phase and post denture insertion adaptive phase, each done before and after chewing. The results obtained were statistically evaluated. RESULTS Power Spectral Density (PSD) values increased from edentulous phase to post denture insertion adaption phase. The data were grouped as edentulous phase before chewing (EEG p1-0.0064), edentulous phase after chewing (EEG p2-0.0073), post denture insertion adaptive phase before chewing (EEG p3-0.0077), and post denture insertion adaptive phase after chewing (EEG p4-0.0096). The acquired values were statistically analyzed using paired t-test, which showed statistically significant results (P<.05). CONCLUSION This pilot study showed functional improvement in brain function of edentulous patients with complete dentures rehabilitation. PMID:27350852
True CMB Power Spectrum Estimation
Paykari, P; Fadili, M J
2012-01-01
The cosmic microwave background (CMB) power spectrum is a powerful cosmological probe as it entails almost all the statistical information of the CMB perturbations. Having access to only one sky, the CMB power spectrum measured by our experiments is only a realization of the true underlying angular power spectrum. In this paper we aim to recover the true underlying CMB power spectrum from the one realization that we have without a need to know the cosmological parameters. The sparsity of the CMB power spectrum is first investigated in two dictionaries; Discrete Cosine Transform (DCT) and Wavelet Transform (WT). The CMB power spectrum can be recovered with only a few percentage of the coefficients in both of these dictionaries and hence is very compressible in these dictionaries. We study the performance of these dictionaries in smoothing a set of simulated power spectra. Based on this, we develop a technique that estimates the true underlying CMB power spectrum from data, i.e. without a need to know the cosmo...
Rota, S; Bel, J; Guzzo, L; Peacock, J A; Wilson, M J; Pezzotta, A; de la Torre, S; Garilli, B; Bolzonella, M; Scodeggio, M; Abbas, U; Adami, C; Bottini, D; Cappi, A; Cucciati, O; Davidson, I; Franzetti, P; Fritz, A; Iovino, A; Krywult, J; Brun, V Le; Fèvre, O Le; Mascagni, D; Małek, K; Marulli, F; Percival, W J; Polletta, M; Pollo, A; Tasca, L A M; Tojeiro, R; Vergani, D; Zanichelli, A; Arnouts, S; Branchini, E; Coupon, J; De Lucia, G; Ilbert, O; Moscardini, L; Moutard, T
2016-01-01
We use the final catalogue of the VIMOS Public Extragalactic Redshift Survey (VIPERS) to measure the power spectrum of the galaxy distribution at high redshift, presenting results that extend beyond $z=1$ for the first time. We apply an FFT technique to four independent sub-volumes comprising a total of $51,728$ galaxies at $0.6
Energy Technology Data Exchange (ETDEWEB)
Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Northwestern U.; Shapiro, Charles; /Chicago U. /KICP, Chicago; White, Martin J.; /UC, Berkeley, Astron.
2005-08-01
Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.
Energy Technology Data Exchange (ETDEWEB)
Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr. /Northwestern U.; Shapiro, Charles; /Chicago U. /KICP, Chicago; White, Martin J.; /UC, Berkeley, Astron.
2005-08-01
Measurements of ellipticities of background galaxies are sensitive to the reduced shear, the cosmic shear divided by (1-{kappa}) where {kappa} is the projected density field. They compute the difference between shear and reduced shear both analytically and with simulations. The difference becomes more important an smaller scales, and will impact cosmological parameter estimation from upcoming experiments. A simple recipe is presented to carry out the required correction.
Primordial power spectrum from Planck
Hazra, Dhiraj Kumar; Souradeep, Tarun
2014-01-01
Using modified Richardson-Lucy algorithm we reconstruct the primordial power spectrum (PPS) from Planck Cosmic Microwave Background (CMB) temperature anisotropy data. In our analysis we use different combinations of angular power spectra from Planck to reconstruct the shape of the primordial power spectrum and locate possible features. Performing an extensive error analysis we found the dip near $\\ell\\sim750-850$ represents the most prominent feature in the data. Feature near $\\ell\\sim1800-2000$ is detectable with high confidence only in 217 GHz spectrum and is apparently consequence of a small systematic as described in the revised Planck 2013 papers. Fixing the background cosmological parameters and the foreground nuisance parameters to their best fit baseline values, we report that the best fit power law primordial power spectrum is consistent with the reconstructed form of the PPS at 2$\\sigma$ C.L. of the estimated errors (apart from the local features mentioned above). As a consistency test, we found the...
Energy Technology Data Exchange (ETDEWEB)
Mueller, Martin; /SLAC
2010-12-16
The study of the power density spectrum (PDS) of fluctuations in the X-ray flux from active galactic nuclei (AGN) complements spectral studies in giving us a view into the processes operating in accreting compact objects. An important line of investigation is the comparison of the PDS from AGN with those from galactic black hole binaries; a related area of focus is the scaling relation between time scales for the variability and the black hole mass. The PDS of AGN is traditionally modeled using segments of power laws joined together at so-called break frequencies; associations of the break time scales, i.e., the inverses of the break frequencies, with time scales of physical processes thought to operate in these sources are then sought. I analyze the Method of Light Curve Simulations that is commonly used to characterize the PDS in AGN with a view to making the method as sensitive as possible to the shape of the PDS. I identify several weaknesses in the current implementation of the method and propose alternatives that can substitute for some of the key steps in the method. I focus on the complications introduced by uneven sampling in the light curve, the development of a fit statistic that is better matched to the distributions of power in the PDS, and the statistical evaluation of the fit between the observed data and the model for the PDS. Using archival data on one AGN, NGC 3516, I validate my changes against previously reported results. I also report new results on the PDS in NGC 4945, a Seyfert 2 galaxy with a well-determined black hole mass. This source provides an opportunity to investigate whether the PDS of Seyfert 1 and Seyfert 2 galaxies differ. It is also an attractive object for placement on the black hole mass-break time scale relation. Unfortunately, with the available data on NGC 4945, significant uncertainties on the break frequency in its PDS remain.
Power Spectrum of Generalized Fractional Gaussian Noise
Directory of Open Access Journals (Sweden)
Ming Li
2013-01-01
Full Text Available Recently, we introduced a type of autocorrelation function (ACF to describe a long-range dependent (LRD process indexed with two parameters, which takes standard fractional Gaussian noise (fGn for short as a special case. For simplicity, we call it the generalized fGn (GfGn. This short paper gives the power spectrum density function (PSD of GfGn.
Enhancing the Cosmic Shear Power Spectrum
Simpson, Fergus; Heymans, Catherine; Jimenez, Raul; Verde, Licia
2015-01-01
Applying a transformation to a non-Gaussian field can enhance the information content of the resulting power spectrum, by reducing the correlations between Fourier modes. In the context of weak gravitational lensing, it has been shown that this gain in information content is significantly compromised by the presence of shape noise. We apply clipping to mock convergence fields, a technique which is known to be robust in the presence of noise and has been successfully applied to galaxy number density fields. When analysed in isolation the resulting convergence power spectrum returns degraded constraints on cosmological parameters. However substantial gains can be achieved by performing a combined analysis of the power spectra derived from both the original and transformed fields. Even in the presence of realistic levels of shape noise, we demonstrate that this approach is capable of reducing the area of likelihood contours within the $\\Omega_m - \\sigma_8$ plane by more than a factor of three.
Spectrum of Wind Power Fluctuations
Bandi, M. M.
2017-01-01
Wind power fluctuations for an individual turbine and plant have been widely reported to follow the Kolmogorov spectrum of atmospheric turbulence; both vary with a fluctuation time scale τ as τ2 /3. Yet, this scaling has not been explained through turbulence theory. Using turbines as probes of turbulence, we show the τ2 /3 scaling results from a large scale influence of atmospheric turbulence. Owing to this long-range influence spanning 100s of kilometers, when power from geographically distributed wind plants is summed into aggregate power at the grid, fluctuations average (geographic smoothing) and their scaling steepens from τ2 /3→τ4 /3, beyond which further smoothing is not possible. Our analysis demonstrates grids have already reached this τ4 /3 spectral limit to geographic smoothing.
Power Spectrum Estimation. I. Basics
Hamilton, A. J. S.
This chapter and its companion form an extended version of notes provided to participants in the Valencia September 2004 summer school on Data Analysis in Cosmology. The lectures offer a pedagogical introduction to the problem of estimating the power spectrum from galaxy surveys. The intention is to focus on concepts rather than on technical detail, but enough mathematics is provided to point the student in the right direction. This first lecture presents background material. It collects some essential definitions, discusses traditional methods for measuring power, notably the Feldman-Kaiser-Peacock [2] method, and introduces Bayesian analysis, Fisher matrices, and maximum likelihood. For pedagogy and brevity, several derivations are set as exercises for the reader. At the summer school, multiple choice questions, included herein, were used to convey some didactic ideas, and provoked a little lively debate.
Power Spectrum Estimation I. Basics
Hamilton, A J S
2005-01-01
This paper and its companion form an extended version of notes provided to participants in the Valencia September 2004 summer school on Data Analysis in Cosmology. The papers offer a pedagogical introduction to the problem of estimating the power spectrum from galaxy surveys. The intention is to focus on concepts rather than on technical detail, but enough mathematics is provided to point the student in the right direction. This first paper presents background material. It collects some essential definitions, discusses traditional methods for measuring power, notably the Feldman-Kaiser-Peacock (1994) method, and introduces Bayesian analysis, Fisher matrices, and maximum likelihood. For pedagogy and brevity, several derivations are set as exercises for the reader. At the summer school, multiple choice questions, included herein, were used to convey some didactic ideas, and provoked a little lively debate.
PWM Converter Power Density Barriers
Kolar, Johann W.; Drofenik, Uwe; Biela, Juergen; Heldwein, Marcelo; Ertl, Hans; Friedli, Thomas; Round, Simon
Power density of power electronic converters has roughly doubled every 10 years since 1970. Behind this trajectory is the continuous advancement of power semiconductor devices, which has increased the converter switching frequencies by a factor of 10 every decade. However, today's cooling concepts and passive components are major barriers for a continuation of this trend. To identify such technological barriers, this paper investigates the volume of the cooling system and passive components as a function of the switching frequency for power electronic converters and determines the switching frequency that minimizes the total volume. A power density limit of 28kW/dm3 at 300kHz is calculated for an isolated DC-DC converter, 44kW/dm3 at 820kHz for a three-phase unity power factor PWM rectifier, and 26kW/dm3 at 21kHz for a sparse matrix converter. For single-phase AC-DC conversion a general limit of 35kW/dm3 results from the DC link capacitor. These power density limits highlight the need to broaden the scope of power electronics research to include cooling systems, high frequency electromagnetics, interconnection and packaging technology, and multi-domain modelling and simulation to ensure further advancement along the power density trajectory.
Toward optimal cluster power spectrum analysis
Smith, Robert E
2014-01-01
The power spectrum of galaxy clusters is an important probe of the cosmological model. In this paper we determine the optimal weighting scheme for maximizing the signal-to-noise ratio for such measurements. We find a closed form analytic expression for the optimal weights. Our expression takes into account: cluster mass, finite survey volume effects, survey masking, and a flux limit. The implementation of this weighting scheme requires knowledge of the measured cluster masses, and analytic models for the bias and space-density of clusters as a function of mass and redshift. Recent studies have suggested that the optimal method for reconstruction of the matter density field from a set of clusters is mass-weighting (Seljak et al 2009, Hamaus et al 2010, Cai et al 2011). We compare our optimal weighting scheme with this approach and also with the original power spectrum scheme of Feldman et al (1994). We show that our optimal weighting scheme outperforms these approaches for both volume- and flux-limited cluster...
Density fluctuation spectrum in whistler turbulence
Energy Technology Data Exchange (ETDEWEB)
Shaikh, Dastgeer, E-mail: dastgeer.shaikh@uah.ed [Department of Physics and Center for Space Plasma and Aeronomy Research, University of Alabama in Huntsville, Huntsville, Alabama 35899 (United States)
2010-05-31
We develop a nonlinear two-dimensional fluid model of whistler turbulence that includes effect of electron fluid density perturbations. The latter is coupled nonlinearly with wave magnetic field. This coupling leads essentially to finite compressibility effects in whistler turbulence model. We find from our simulations that despite strong compressibility effects, the density fluctuations follow the evolution of the wave magnetic field fluctuations. In a characteristic regime where large scale whistlers are predominant, the coupled density fluctuations are found to follow a Kolmogorov-like phenomenology in the inertial range turbulence. Consequently, the turbulent energy is dominated by the large scale (compared to electron inertial length) eddies and it follows a Kolmogorov-like k{sup -7/3} spectrum, where k is a characteristic wavenumber.
Precision Prediction of the Log Power Spectrum
Repp, Andrew
2016-01-01
At translinear scales, the log power spectrum captures significantly more cosmological information than the standard power spectrum. At high wavenumbers $k$, the cosmological information in the standard power spectrum $P(k)$ fails to increase in proportion to $k$ due to correlations between large- and small-scale modes. As a result, $P(k)$ suffers from an information plateau on these translinear scales, so that analysis with the standard power spectrum cannot access the information contained in these small-scale modes. The log power spectrum $P_A(k)$, on the other hand, captures the majority of this otherwise lost information. Until now there has been no means of predicting the amplitude of the log power spectrum apart from cataloging the results of simulations. We here present a cosmology-independent prescription for the log power spectrum, and we find this prescription to display accuracy comparable to that of Smith et al. (2003), over a range of redshifts and smoothing scales, and for wavenumbers up to $1....
The power spectrum of IRAS galaxies
Tadros, H; Tadros, Helen; Efstathiou, George
1995-01-01
We estimate the three-dimensional power spectrum of IRAS galaxies from the QDOT and 1.2Jy redshift surveys. We use identical estimators for both surveys and show how the results depend on the weights assigned to the galaxies. The power spectrum for the QDOT survey is steeper and has a higher amplitude at wavenumbers k \\sim 0.05\\; h {\\rm Mpc}^{-1} (where h is Hubble's constant in units of 100 \\kmsmpc) than the power spectrum derived from the 1.2Jy sample. However, the QDOT power spectrum is sensitive to a small number of galaxies in the Hercules supercluster, in agreement with a recent analysis of galaxy counts in cells in these surveys. We argue that the QDOT results are an upward fluctuation. We combine the two surveys to derive our best estimate of the power spectrum of IRAS galaxies. This is shallower and has a lower amplitude on scales \\simlt 0.1 h {\\rm Mpc}^{-1} than the power spectrum derived by Feldman \\et (1994) from the QDOT survey alone. The power spectrum of the combined surveys is well described b...
Tensor power spectrum and disformal transformations
Fumagalli, Jacopo; Postma, Marieke
2016-01-01
In a general effective theory description of inflation a disformal transformation can be used to set the tensor sound speed to one. After the transformation, the tensor power spectrum then automatically only depends on the Hubble parameter. We show that this disformal transformation, however, is nothing else than a change of units. It is a very useful tool for simplifying and interpreting computations, but it cannot change any physics. While the apparent parametrical dependence of the tensor power spectrum does change under a disformal transformation, the physics described is frame invariant. We further illustrate the frame invariance of the tensor power spectrum by writing it exclusively in terms of separately invariant quantities.
Subsampling for graph power spectrum estimation
Chepuri, Sundeep Prabhakar
2016-10-06
In this paper we focus on subsampling stationary random signals that reside on the vertices of undirected graphs. Second-order stationary graph signals are obtained by filtering white noise and they admit a well-defined power spectrum. Estimating the graph power spectrum forms a central component of stationary graph signal processing and related inference tasks. We show that by sampling a significantly smaller subset of vertices and using simple least squares, we can reconstruct the power spectrum of the graph signal from the subsampled observations, without any spectral priors. In addition, a near-optimal greedy algorithm is developed to design the subsampling scheme.
The Spectrum of Wind Power Fluctuations
Bandi, Mahesh
2016-11-01
Wind is a variable energy source whose fluctuations threaten electrical grid stability and complicate dynamical load balancing. The power generated by a wind turbine fluctuates due to the variable wind speed that blows past the turbine. Indeed, the spectrum of wind power fluctuations is widely believed to reflect the Kolmogorov spectrum; both vary with frequency f as f - 5 / 3. This variability decreases when aggregate power fluctuations from geographically distributed wind farms are averaged at the grid via a mechanism known as geographic smoothing. Neither the f - 5 / 3 wind power fluctuation spectrum nor the mechanism of geographic smoothing are understood. In this work, we explain the wind power fluctuation spectrum from the turbine through grid scales. The f - 5 / 3 wind power fluctuation spectrum results from the largest length scales of atmospheric turbulence of order 200 km influencing the small scales where individual turbines operate. This long-range influence spatially couples geographically distributed wind farms and synchronizes farm outputs over a range of frequencies and decreases with increasing inter-farm distance. Consequently, aggregate grid-scale power fluctuations remain correlated, and are smoothed until they reach a limiting f - 7 / 3 spectrum. This work was funded by the Collective Interactions Unit, OIST Graduate University, Japan.
Spectra: Time series power spectrum calculator
Gallardo, Tabaré
2017-01-01
Spectra calculates the power spectrum of a time series equally spaced or not based on the Spectral Correlation Coefficient (Ferraz-Mello 1981, Astron. Journal 86 (4), 619). It is very efficient for detection of low frequencies.
Power spectrum analysis for optical tweezers
DEFF Research Database (Denmark)
Berg-Sørensen, K.; Flyvbjerg, H.
2004-01-01
the Lorentzian provides. This is achieved using old and new theory for Brownian motion in an incompressible fluid, and new results for a popular photodetection system. The trap and photodetection system are then calibrated simultaneously in a manner that makes optical tweezers a tool of precision for force......The force exerted by an optical trap on a dielectric bead in a fluid is often found by fitting a Lorentzian to the power spectrum of Brownian motion of the bead in the trap. We present explicit functions of the experimental power spectrum that give the values of the parameters fitted, including...... obtain perfect fits and calibrate tweezers with less than 1% error when the trapping force is not too strong. Relatively strong traps have power spectra that cannot be fitted properly with any Lorentzian, we find. This underscores the need for better understanding of the power spectrum than...
Primordial power spectrum features and consequences
Goswami, Gaurav
2014-01-01
The present Cosmic Microwave Background (CMB) temperature and polarization anisotropy data is consistent with not only a power law scalar primordial power spectrum (PPS) with a small running but also with the scalar PPS having very sharp features. This has motivated inflationary models with such sharp features. Recently, even the possibility of having nulls in the power spectrum (at certain scales) has been considered. The existence of these nulls has been shown in linear perturbation theory. What shall be the effect of higher order corrections on such nulls? Inspired by this question, we attempt to calculate quantum radiative corrections to the Fourier transform of the two-point function in a toy field theory and address the issue of how these corrections to the power spectrum behave in models in which the tree-level power spectrum has a sharp dip (but not a null). In particular, we consider the possibility of the relative enhancement of radiative corrections in a model in which the tree-level spectrum goes ...
The Effect of Curvaton Decay on the Primordial Power Spectrum
Firouzjahi, Hassan; Malik, Karim; Zarei, Moslem
2012-01-01
We study the effect of curvaton decay on the primordial power spectrum. Using analytical approximations and also numerical calculations, we find that the power spectrum is enhanced during the radiation dominated era after the curvaton decay. The amplitude of the Bardeen potential is controlled by the fraction of the energy density in the curvaton at the time of curvaton decay. We show that the enhancement in the amplitude of the primordial curvature perturbation is, however, not large enough to lead to primordial black hole overproduction on scales which re-enter the horizon after the time of curvaton decay.
Power spectrum analysis for optical tweezers
DEFF Research Database (Denmark)
Berg-Sørensen, K.; Flyvbjerg, H.
2004-01-01
The force exerted by an optical trap on a dielectric bead in a fluid is often found by fitting a Lorentzian to the power spectrum of Brownian motion of the bead in the trap. We present explicit functions of the experimental power spectrum that give the values of the parameters fitted, including...... error bars and correlations, for the best such chi(2) fit in a given frequency range. We use these functions to determine the information content of various parts of the power spectrum, and find, at odds with lore, much information at relatively high frequencies. Applying the method to real data, we...... the Lorentzian provides. This is achieved using old and new theory for Brownian motion in an incompressible fluid, and new results for a popular photodetection system. The trap and photodetection system are then calibrated simultaneously in a manner that makes optical tweezers a tool of precision for force...
Electronic DC transformer with high power density
Pavlovský, M.
2006-01-01
This thesis is concerned with the possibilities of increasing the power density of high-power dc-dc converters with galvanic isolation. Three cornerstones for reaching high power densities are identified as: size reduction of passive components, reduction of losses particularly in active components
A new method of measuring the peculiar velocity power spectrum
Zhang, P; Juszkiewicz, R; Feldman, H A; Zhang, Pengjie; Stebbins, Albert; Juszkiewicz, Roman; Feldman, Hume
2004-01-01
We show that by directly correlating the cluster kinetic Sunyaev Zeldovich (KSZ) flux, the cluster peculiar velocity power spectrum can be measured to $\\sim 10%$ accuracy by future large sky coverage KSZ surveys. This method is almost free of systemics entangled in the usual velocity inversion method. The direct correlation brings extra information of density and velocity clustering. We utilize these information to construct two indicators of the Hubble constant and comoving angular distance and propose a novel method to constrain cosmology.
CHIPS: The Cosmological HI Power Spectrum Estimator
Trott, Cathryn M; Procopio, Pietro; Wayth, Randall B; Mitchell, Daniel A; McKinley, Benjamin; Tingay, Steven J; Barry, N; Beardsley, A P; Bernardi, G; Bowman, Judd D; Briggs, F; Cappallo, R J; Carroll, P; de Oliveira-Costa, A; Dillon, Joshua S; Ewall-Wice, A; Feng, L; Greenhill, L J; Hazelton, B J; Hewitt, J N; Hurley-Walker, N; Johnston-Hollitt, M; Jacobs, Daniel C; Kaplan, D L; Kim, HS; Lenc, E; Line, J; Loeb, A; Lonsdale, C J; Morales, M F; Morgan, E; Neben, A R; Thyagarajan, Nithyanandan; Oberoi, D; Offringa, A R; Ord, S M; Paul, S; Pober, J C; Prabu, T; Riding, J; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Sullivan, I S; Tegmark, M; Webster, R L; Williams, A; Williams, C L; Wu, C; Wyithe, J S B
2016-01-01
Detection of the cosmological neutral hydrogen signal from the Epoch of Reionization, and estimation of its basic physical parameters, is the principal scientific aim of many current low-frequency radio telescopes. Here we describe the Cosmological HI Power Spectrum Estimator (CHIPS), an algorithm developed and implemented with data from the Murchison Widefield Array (MWA), to compute the two-dimensional and spherically-averaged power spectrum of brightness temperature fluctuations. The principal motivations for CHIPS are the application of realistic instrumental and foreground models to form the optimal estimator, thereby maximising the likelihood of unbiased signal estimation, and allowing a full covariant understanding of the outputs. CHIPS employs an inverse-covariance weighting of the data through the maximum likelihood estimator, thereby allowing use of the full parameter space for signal estimation ("foreground suppression"). We describe the motivation for the algorithm, implementation, application to ...
The Effect of Massive Neutrinos on Matter Power Spectrum
Agarwal, Shankar
2010-01-01
We investigate the impact of massive neutrinos on the distribution of matter in the semi-nonlinear regime (0.1
Considering Air Density in Wind Power Production
Farkas, Zénó
2011-01-01
In the wind power production calculations the air density is usually considered as constant in time. Using the CIPM-2007 equation for the density of moist air as a function of air temperature, air pressure and relative humidity, we show that it is worth taking the variation of the air density into account, because higher accuracy can be obtained in the calculation of the power production for little effort.
Power Spectrum Estimation from Peculiar Velocity Catalogues
Macaulay, Edward; Ferreira, Pedro G; Jaffe, Andrew H; Agarwal, Shankar; Hudson, Michael J; Watkins, Richard
2011-01-01
The peculiar velocities of galaxies are an inherently valuable cosmological probe, providing an unbiased estimate of the distribution of matter on scales much larger than the depth of the survey. Much research interest has been motivated by the high dipole moment of our local peculiar velocity field, which suggests a large scale excess in the matter power spectrum, and can appear to be in some tension with the LCDM model. We use a composite catalogue of 4,537 peculiar velocity measurements with a characteristic depth of 33 h-1 Mpc to estimate the matter power spectrum. We compare the constraints with this method, directly studying the full peculiar velocity catalogue, to results from Macaulay et al. (2011), studying minimum variance moments of the velocity field, as calculated by Watkins, Feldman & Hudson (2009) and Feldman, Watkins & Hudson (2010). We find good agreement with the LCDM model on scales of k > 0.01 h Mpc-1. We find an excess of power on scales of k < 0.01 h Mpc-1, although with a 1 s...
Chluba, Jens; Ben-Dayan, Ido
2012-01-01
In the early Universe, energy stored in small-scale density perturbations is quickly dissipated by Silk-damping, a process that inevitably generates mu- and y-type spectral distortions of the cosmic microwave background (CMB). These spectral distortions depend on the shape and amplitude of the primordial power spectrum at wavenumbers k < 10^4 Mpc^{-1}. Here we study constraints on the primordial power spectrum derived from COBE/FIRAS and forecasted for PIXIE. We show that measurements of mu and y impose strong bounds on the integrated small-scale power, and we demonstrate how to compute these constraints using k-space window functions that account for the effects of thermalization and dissipation physics. We show that COBE/FIRAS places a robust upper limit on the amplitude of the small-scale power spectrum. This limit is about three orders of magnitude stronger than the one derived from primordial black holes in the same scale range. Furthermore, this limit could be improved by another three orders of magn...
The Small-Scale Power Spectrum of Cold Dark Matter
Loeb, A; Loeb, Abraham; Zaldarriaga, Matias
2005-01-01
One of the best motivated hypotheses in cosmology states that most of the matter in the universe is in the form of weakly-interacting massive particles that decoupled early in the history of the universe and cooled adiabatically to an extremely low temperature. Nevertheless, the finite temperature and horizon scales at which these particles decoupled imprint generic signatures on their small scales density fluctuations. We show that the previously recognized cut-off in the fluctuation power-spectrum due to free-streaming of particles at the thermal speed of decoupling, is supplemented by acoustic oscillations owing to the initial coupling between the cold dark matter (CDM) and the radiation field. The power-spectrum oscillations appear on the scale of the horizon at thermal decoupling which corresponds to a mass scale of \\~10^{-4}*(T_d/10MeV)^{-3} solar masses for a CDM decoupling temperature T_d. The suppression of the power-spectrum on smaller scales by the acoustic oscillations is physically independent fr...
Power spectrum analysis for defect screening in integrated circuit devices
Tangyunyong, Paiboon; Cole Jr., Edward I.; Stein, David J.
2011-12-01
A device sample is screened for defects using its power spectrum in response to a dynamic stimulus. The device sample receives a time-varying electrical signal. The power spectrum of the device sample is measured at one of the pins of the device sample. A defect in the device sample can be identified based on results of comparing the power spectrum with one or more power spectra of the device that have a known defect status.
Einasto profiles and the dark matter power spectrum
Ludlow, Aaron D.; Angulo, Raúl E.
2017-02-01
We study the mass accretion histories (MAHs) and density profiles of dark matter haloes using N-body simulations of self-similar gravitational clustering from scale-free power spectra, P(k) ∝ kn. We pay particular attention to the density profile curvature, which we characterize using the shape parameter, α, of an Einasto profile. In agreement with previous findings, our results suggest that, despite vast differences in their MAHs, the density profiles of virialized haloes are remarkably alike. Nonetheless, clear departures from self-similarity are evident: For a given spectral index, α increases slightly but systematically with `peak height', ν ≡ δsc/σ(M, z), regardless of mass or redshift. More importantly, however, the `α-ν' relation depends on n: The steeper the initial power spectrum, the more gradual the curvature of both the mean MAHs and mean density profiles. These results are consistent with previous findings connecting the shapes of halo mass profiles and MAHs, and imply that dark matter haloes are not structurally self-similar but, through the merger history, retain a memory of the linear density field from which they form.
Power Spectrum Estimation of Randomly Sampled Signals
DEFF Research Database (Denmark)
Velte, Clara M.; Buchhave, Preben; K. George, William
2014-01-01
The random, but velocity dependent, sampling of the LDA presents non-trivial signal processing challengesdue to the high velocity bias and the arbitrariness of particle path through the measuring volume, among other factors.To obtain the desired non-biased statistics, it has previously been shown...... analytically as well as empirically thatresidence time weighting is the suitable choice. Unfortunately, due to technical problems related to the processors providing erroneous measurements of the residence times, this previously widely accepted theory has been questioned and instead a wide spectrum...... of alternative methods attempting to produce correct power spectra have been invented andtested. The objective of the current study is to create a simple computer generated signal for baseline testing of residence time weighting and some of the most commonly proposed algorithms (or algorithms which most...
Directory of Open Access Journals (Sweden)
S. Dastgeer
2005-01-01
Full Text Available Interstellar scintillation and angular radio wave broadening measurements show that interstellar and solar wind (electron density fluctuations exhibit a Kolmogorov-like k-5/3 power spectrum extending over many decades in wavenumber space. The ubiquity of the Kolmogorov-like interstellar medium (ISM density spectrum led to an explanation based on coupling incompressible magnetohydrodynamic (MHD fluctuations to density fluctuations through a 'pseudosound' relation within the context of 'nearly incompressible' (NI hydrodynamics (HD and MHD models. The NI theory provides a fundamentally different explanation for the observed ISM density spectrum in that the density fluctuations can be a consequence of passive scalar convection due to background incompressible fluctuations. The theory further predicts generation of long-scale structures and various correlations between the density, temperature and the (magneto acoustic as well as convective pressure fluctuations in the compressible ISM fluids in different thermal regimes that are determined purely by the thermal fluctuation level. In this paper, we present the results of our two dimensional nonlinear fluid simulations, exploring various nonlinear aspects that lead to inertial range ISM turbulence within the context of a NI hydrodymanics model. In qualitative agreement with the NI predictions and the in-situ observations, we find that i the density fluctuations exhibit a Kolmogorov-like spectrum via a passive convection in the field of the background incompressible fluctuations, ii the compressible ISM fluctuations form long scale flows and structures, and iii the density and the temperature fluctuations are anti-correlated.
Calculated power distribution of a thermionic, beryllium oxide reflected, fast-spectrum reactor
Mayo, W.; Lantz, E.
1973-01-01
A procedure is developed and used to calculate the detailed power distribution in the fuel elements next to a beryllium oxide reflector of a fast-spectrum, thermionic reactor. The results of the calculations show that, although the average power density in these outer fuel elements is not far from the core average, the power density at the very edge of the fuel closest to the beryllium oxide is about 1.8 times the core avearge.
Minimally Parametric Power Spectrum Reconstruction from the Lyman-alpha Forest
Bird, Simeon; Viel, Matteo; Verde, Licia
2010-01-01
Current results from the Lyman alpha forest assume that the primordial power spectrum of density perturbations follows a simple power law form. We present the first analysis of Lyman alpha data to study the effect of relaxing this strong assumption on primordial and astrophysical constraints. We perform a large suite of numerical simulations, using them to calibrate a minimally parametric framework for describing the power spectrum. Combined with cross-validation, a statistical technique which prevents over-fitting of the data, this framework allows us to reconstruct the power spectrum shape without strong prior assumptions. We find no evidence for deviation from scale-invariance; our analysis also shows that current Lyman alpha data do not have sufficient statistical power to robustly probe the shape of the power spectrum at these scales. In contrast, the ongoing Baryon Oscillation Sky Survey (BOSS) will be able to do so with high precision. Furthermore, this near-future data will be able to break degeneraci...
Institute of Scientific and Technical Information of China (English)
张耿; 李杰; 杨子敬
2011-01-01
Track irregularity is the main excitation source to vibration of the maglev train, and it has direct influence on stability and ride quality of the train. The statistical specimens of track irregularities are collected from the TangShan low-speed maglev experimental line on the basis of the stationarity tests of the specimens, the Fast Fourier Transform(FFT) method was used to evaluate the spectra of the whole specimen space. Distribution of track irregularities in space wavelengths was found. Analysis results show that the structural parameters, installation precision and rolling technique of tracks are the main causes of track irregularity. Referring to the mature PSD( power spectrum density) expressions published athome and abroatl, the set fitting formulas of PSD for low-speed maglev railway lines were proposed. The parameter values of PSD fitting curves for low-speed maglev track irregularities were obtained by use of the damping curve-fitting algorithm in the least-squares sense. Significaul reference is provided to study on track irregularity PSD of low-speed maglev railway lines.%轨道不平顺是磁浮列车振动的主要激扰源,直接关系到列车运行的稳定性和舒适性.文章基于唐山低速磁浮试验线实测的轨道不平顺数据,采用周期图法进行样本空间的谱估计,得到轨道不平顺在各空间波长的分布.分析结果表明,轨道本身结构参数、轨道安装精度和F轨的轧制工艺是产生轨道不平顺的主要原因.参考国内外成熟的铁路轨道谱线表达形式,得到低速磁浮轨道谱的拟合曲线公式,应用阻尼最小二乘算法拟合轨道谱表达式的参数,对于研究我国磁浮轨道不平顺功率谱有重要的参考价值.
High power density carbonate fuel cell
Energy Technology Data Exchange (ETDEWEB)
Yuh, C.; Johnsen, R.; Doyon, J.; Allen, J. [Energy Research Corp., Danbury, CT (United States)
1996-12-31
Carbonate fuel cell is a highly efficient and environmentally clean source of power generation. Many organizations worldwide are actively pursuing the development of the technology. Field demonstration of multi-MW size power plant has been initiated in 1996, a step toward commercialization before the turn of the century, Energy Research Corporation (ERC) is planning to introduce a 2.85MW commercial fuel cell power plant with an efficiency of 58%, which is quite attractive for distributed power generation. However, to further expand competitive edge over alternative systems and to achieve wider market penetration, ERC is exploring advanced carbonate fuel cells having significantly higher power densities. A more compact power plant would also stimulate interest in new markets such as ships and submarines where space limitations exist. The activities focused on reducing cell polarization and internal resistance as well as on advanced thin cell components.
Wind speed power spectrum analysis for Bushland, Texas
Energy Technology Data Exchange (ETDEWEB)
Eggleston, E.D. [USDA-Agricultural Research Service, Bushland, TX (United States)
1996-12-31
Numerous papers and publications on wind turbulence have referenced the wind speed spectrum presented by Isaac Van der Hoven in his article entitled Power Spectrum of Horizontal Wind Speed Spectrum in the Frequency Range from 0.0007 to 900 Cycles per Hour. Van der Hoven used data measured at different heights between 91 and 125 meters above the ground, and represented the high frequency end of the spectrum with data from the peak hour of hurricane Connie. These facts suggest we should question the use of his power spectrum in the wind industry. During the USDA - Agricultural Research Service`s investigation of wind/diesel system power storage, using the appropriate wind speed power spectrum became a significant issue. We developed a power spectrum from 13 years of hourly average data, 1 year of 5 minute average data, and 2 particularly gusty day`s 1 second average data all collected at a height of 10 meters. While the general shape is similar to the Van der Hoven spectrum, few of his peaks were found in the Bushland spectrum. While higher average wind speeds tend to suggest higher amplitudes in the high frequency end of the spectrum, this is not always true. Also, the high frequency end of the spectrum is not accurately described by simple wind statistics such as standard deviation and turbulence intensity. 2 refs., 5 figs., 1 tab.
Contribution of strong discontinuities to the power spectrum of the solar wind.
Borovsky, Joseph E
2010-09-10
Eight and a half years of magnetic field measurements (2(22) samples) from the ACE spacecraft in the solar wind at 1 A.U. are analyzed. Strong (large-rotation-angle) discontinuities in the solar wind are collected and measured. An artificial time series is created that preserves the timing and amplitudes of the discontinuities. The power spectral density of the discontinuity series is calculated and compared with the power spectral density of the solar-wind magnetic field. The strong discontinuities produce a power-law spectrum in the "inertial subrange" with a spectral index near the Kolmogorov -5/3 index. The discontinuity spectrum contains about half of the power of the full solar-wind magnetic field over this "inertial subrange." Warnings are issued about the significant contribution of discontinuities to the spectrum of the solar wind, complicating interpretation of spectral power and spectral indices.
BB mode angular power spectrum of CMB from massive gravity
Malsawmtluangi, N
2016-01-01
The primordial massive gravitational waves are placed in the squeezed vacuum state and corresponding $BB$-mode correlation angular power spectrum of the cosmic microwave background is obtained for various slow roll inflation models. The angular power spectrum is compared with the limit of BICEP2/Keck and Planck joint analysis data and the hybrid inflation model is found favorable.
Noncommutative Geometry and the Primordial Dipolar Imaginary Power Spectrum
Jain, P
2014-01-01
We argue that an anisotropic dipolar imaginary primordial power spectrum is possible within the framework of noncommutative space-times. We show that such a spectrum provides a good description of the observed dipole modulation in CMBR data. We extract the corresponding power spectrum from data. The dipole modulation is related to the observed hemispherical anisotropy in CMBR data, which might represent the first signature of quantum gravity.
On the power spectrum of solar surface flows
Rieutord, M; Rincon, F; Malherbe, J -M; Meunier, N; Berger, T; Frank, Z
2009-01-01
The aim of this work is to give new observational constraints on solar surface flows by determining the horizontal scale dependence of the velocity and intensity fields, as represented by their power spectra, and to offer some theoretical guidelines to interpret these spectra. We use long time series of images taken by SOT/Hinode and reconstruct both horizontal (by granule tracking) and vertical (by Doppler effect) velocity fields in a field of view 75x75Mm^2. At small sub-granulation scales, the kinetic energy spectral density associated with vertical motions exhibits a k^{-13/3}-like spectrum, while the intensity fluctuation spectrum follows a k^{-17/3}-like spectrum. We discuss the physical origin of these scalings and argue that they provide a direct observational signature of buoyancy-driven turbulent dynamics in a strongly thermally diffusive regime. In the mesogranulation range and up to a scale of 25Mm, we find that the vertical velocity field amplitude decreases like L^{-3/2} with the horizontal scal...
Relationship between input power and power density of SMA spring
Park, Cheol Hoon; Ham, Sang Yong; Son, Young Su
2016-04-01
The important required characteristics of an artificial muscle for a human arm-like manipulator are high strain and high power density. From this viewpoint, an SMA (shape memory alloy) spring is a good candidate for the actuator of a robotic manipulator that utilizes an artificial muscle. In this study, the maximum power density of an SMA spring was evaluated with respect to the input power. The spring samples were fabricated from SMA wires of different diameters ranging between 0.1 and 0.3 mm. For each diameter, two types of wires with different transition temperatures were used. The relationship between the transition temperature and maximum power density was also evaluated. Each SMA spring was stretched downward by an attached weight and the temperature was increased through the application of an electric current. The displacement, velocity, and temperature of the SMA spring were measured by laser displacement sensors and a thermocouple. Based on the experimental data, it was determined that the maximum power densities of the different SMA springs ranged between 1,300 and 5,500 W/kg. This confirmed the applicability of an SMA spring to human arm-like robotic manipulators. The results of this study can be used as reference for design.
Institute of Scientific and Technical Information of China (English)
Zhang Shiquan; Ge Debiao
2005-01-01
In order to analyze the deleterious effects of Passive InterModulation (PIM) on high power communication satellite systems, the basic concept of PIM is introduced, and an equation for the power spectral density of the n-th order PIM distortion insuch systems is derived by applying flat signal-power spectrum assumption and Fourier transform method. It is indicated that PIM level generally decreases with order and the lowest frequency receive channel in the receive band is the channel of most affected by PIM interference.
Complex spectrum of spin models for finite-density QCD
Nishimura, Hiromichi; Pangeni, Kamal
2016-01-01
We consider the spectrum of transfer matrix eigenvalues associated with Polyakov loops in lattice QCD at strong coupling. The transfer matrix at finite density is non-Hermitian, and its eigenvalues become complex as a manifestation of the sign problem. We show that the symmetry under charge conjugation and complex conjugation ensures that the eigenvalues are either real or part of a complex conjugate pair, and the complex pairs lead to damped oscillatory behavior in Polyakov loop correlation functions, which also appeared in our previous phenomenological models using complex saddle points. We argue that this effect should be observable in lattice simulations of QCD at finite density.
Testing for new physics: neutrinos and the primordial power spectrum
Canac, Nicolas; Aslanyan, Grigor; Abazajian, Kevork N.; Easther, Richard; Price, Layne C.
2016-09-01
We test the sensitivity of neutrino parameter constraints from combinations of CMB and LSS data sets to the assumed form of the primordial power spectrum (PPS) using Bayesian model selection. Significantly, none of the tested combinations, including recent high-precision local measurements of H0 and cluster abundances, indicate a signal for massive neutrinos or extra relativistic degrees of freedom. For PPS models with a large, but fixed number of degrees of freedom, neutrino parameter constraints do not change significantly if the location of any features in the PPS are allowed to vary, although neutrino constraints are more sensitive to PPS features if they are known a priori to exist at fixed intervals in log k. Although there is no support for a non-standard neutrino sector from constraints on both neutrino mass and relativistic energy density, we see surprisingly strong evidence for features in the PPS when it is constrained with data from Planck 2015, SZ cluster counts, and recent high-precision local measurements of H0. Conversely combining Planck with matter power spectrum and BAO measurements yields a much weaker constraint. Given that this result is sensitive to the choice of data this tension between SZ cluster counts, Planck and H0 measurements is likely an indication of unmodeled systematic bias that mimics PPS features, rather than new physics in the PPS or neutrino sector.
Halo Concentration and the Dark Matter Power Spectrum
Huffenberger, Kevin M; Huffenberger, Kevin M.; Seljak, Uros
2003-01-01
We explore the connection between halo concentration and the dark matter power spectrum using the halo model. We fit halo model parameters to non-linear power spectra over a large range of cosmological models. We find that the non-linear evolution of the power spectrum generically prefers the concentration at non-linear mass scale to decrease with the effective slope of the linear power spectrum, in agreement with the direct analysis of the halo structure in different cosmological models. Using these analyses, we compute the predictions for non-linear power spectrum beyond the current resolution of N-body simulations. We find that the halo model predictions are generically below the analytical non-linear models, suggesting that the latter may overestimate the amount of power on small scales.
Power spectrum, correlation function, and tests for luminosity bias in the CfA redshift survey
Park, Changbom; Vogeley, Michael S.; Geller, Margaret J.; Huchra, John P.
1994-01-01
50% of galaxies in volume-limited samples that have M(sub lim) greater than M*. This bias in the power spectrum is independent of scale, consistent with the peaks-bias paradigm for galaxy formation. Second, the distribution of local density around galaxies shows that regions of moderate and high density contain both very bright (M less than M* = -19.2 + 5 log h) and fainter galaxies, but that voids preferentially harbor fainter galaxies (approximately 2 sigma significance level).
Measuring the VIPERS galaxy power spectrum at z∼1
Rota, Stefano; Bel, Julien; Granett, Ben; Guzzo, Luigi
2016-10-01
The VIMOS Public Extragalactic Redshift Survey [VIPERS, Guzzo et al. 2014] is using the VIMOS spectrograph at the ESO VLT to measure redshifts for ~ 100,000 galaxies with IAB < 22.5 and 0.5 < z < 1.2, over an area of 24 deg2 (split over the W1 and W4 fields of CFHTLS). VIPERS currently provides, at such redshifts, the best compromise between volume, number of galaxies and dense spatial sampling. We present here the first estimate of the power spectrum of the galaxy distribution, P(k), at redshifts z ~ 0.75 and z ~ 1, obtained from the ~ 55,000 redshifts of the PDR-1 data release. We discuss first constraints on cosmological quantities, as the matter density and the baryonic fraction, obtained for the first time at an epoch when the Universe was about half its current age.
Towards optimal estimation of the galaxy power spectrum
Smith, Robert E
2015-01-01
The galaxy power spectrum encodes a wealth of information about cosmology and the matter fluctuations. Its unbiased and optimal estimation is therefore of great importance. In this paper we generalise the framework of Feldman et al. (1994) to take into account the fact that galaxies are not simply a Poisson sampling of the underlying dark matter distribution. Besides finite survey-volume effects and flux-limits, our optimal estimation scheme incorporates several of the key tenets of galaxy formation: galaxies form and reside exclusively in dark matter haloes; a given dark matter halo may host several galaxies of various luminosities; galaxies inherit part of their large-scale bias from their host halo. Under these broad assumptions, we prove that the optimal weights "do not" explicitly depend on galaxy luminosity, other than through defining the maximum survey volume and effective galaxy density at a given position. Instead, they depend on the bias associated with the host halo; the first and second factorial...
High Power Density Power Electronic Converters for Large Wind Turbines
DEFF Research Database (Denmark)
Senturk, Osman Selcuk
In large wind turbines (in MW and multi-MW ranges), which are extensively utilized in wind power plants, full-scale medium voltage (MV) multi-level (ML) voltage source converters (VSCs) are being more preferably employed nowadays for interfacing these wind turbines with electricity grids...... assessments of these specific VSCs so that their power densities and reliabilities are quantitatively determined, which requires extensive utilization of the electro-thermal models of the VSCs under investigation. In this thesis, the three-level neutral-point-clamped VSCs (3L-NPC-VSCs), which are classified......-HB-VSCs). As the switch technology for realizing these 3L-VSCs, press-pack IGBTs are chosen to ensure high power density and reliability. Based on the selected 3L-VSCs and switch technology, the converter electro-thermal models are developed comprehensively, implemented practically, and validated via a full-scale 3L...
Measuring the power spectrum of dark matter substructure using strong gravitational lensing
Hezaveh, Yashar; Holder, Gilbert; Kisner, Theodore; Kuhlen, Michael
2014-01-01
In recent years, it has become possible to detect individual dark matter subhalos near strong gravitational lenses. Typically, only the most massive subhalos in the strong lensing region may be detected this way. In this work, we show that strong lenses may also be used to constrain the much more numerous population of lower mass subhalos that are too small to be detected individually. In particular, we show that the power spectrum of projected density fluctuations in galaxy halos can be measured using strong gravitational lensing. We develop the mathematical framework of power spectrum estimation, and test our method on mock observations. We use our results to determine the types of observations required to measure the substructure power spectrum with high significance. We predict that deep observations with current facilities (in particular ALMA) can measure this power spectrum, placing strong constraints on the abundance of dark matter subhalos and the underlying particle nature of dark matter.
The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology
Jacobs, Daniel C.; Hazelton, B. J.; Trott, C. M.; Dillon, Joshua S.; Pindor, B.; Sullivan, I. S.; Pober, J. C.; Barry, N.; Beardsley, A. P.; Bernardi, G.; Bowman, Judd D.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; de Oliveira-Costa, A.; Emrich, D.; Ewall-Wice, A.; Feng, L.; Gaensler, B. M.; Goeke, R.; Greenhill, L. J.; Hewitt, J. N.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper, J. C.; Kim, HS; Kratzenberg, E.; Lenc, E.; Line, J.; Loeb, A.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Neben, A. R.; Thyagarajan, N.; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Paul, S.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Udaya Shankar, N.; Sethi, Shiv K.; Srivani, K. S.; Subrahmanyan, R.; Tegmark, M.; Tingay, S. J.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wu, C.; Wyithe, J. S. B.
2016-07-01
We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple independent data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction, and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregrounds.
The Murchison Widefield Array 21 cm Power Spectrum Analysis Methodology
Jacobs, Daniel C; Trott, C M; Dillon, Joshua S; Pindor, B; Sullivan, I S; Pober, J C; Barry, N; Beardsley, A P; Bernardi, G; Bowman, Judd D; Briggs, F; Cappallo, R J; Carroll, P; Corey, B E; de Oliveira-Costa, A; Emrich, D; Ewall-Wice, A; Feng, L; Gaensler, B M; Goeke, R; Greenhill, L J; Hewitt, J N; Hurley-Walker, N; Johnston-Hollitt, M; Kaplan, D L; Kasper, J C; Kim, H S; Kratzenberg, E; Lenc, E; Line, J; Loeb, A; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Neben, A R; Thyagarajan, N; Oberoi, D; Offringa, A R; Ord, S M; Paul, S; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Tegmark, M; Tingay, S J; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wu, C; Wyithe, J S B
2016-01-01
We present the 21 cm power spectrum analysis approach of the Murchison Widefield Array Epoch of Reionization project. In this paper, we compare the outputs of multiple pipelines for the purpose of validating statistical limits cosmological hydrogen at redshifts between 6 and 12. Multiple, independent, data calibration and reduction pipelines are used to make power spectrum limits on a fiducial night of data. Comparing the outputs of imaging and power spectrum stages highlights differences in calibration, foreground subtraction and power spectrum calculation. The power spectra found using these different methods span a space defined by the various tradeoffs between speed, accuracy, and systematic control. Lessons learned from comparing the pipelines range from the algorithmic to the prosaically mundane; all demonstrate the many pitfalls of neglecting reproducibility. We briefly discuss the way these different methods attempt to handle the question of evaluating a significant detection in the presence of foregr...
Large-scale power-spectrum from peculiar velocities
Kolatt, T S; Kolatt, Tsafrir; Dekel, Avishai
1995-01-01
The power spectrum (PS) of {\\it mass} density fluctuations, in the range 0.05 \\leq k \\leq 0.2 \\ihmpc, is derived from the Mark III catalog of peculiar velocities of galaxies, independent of ``biasing". It is computed from the density field as recovered by POTENT with Gaussian smoothing of 12\\hmpc, within a sphere of radius \\sim 60 \\hmpc about the Local Group. The density is weighted inversely by the errors. The PS is corrected for the effects of smoothing, random errors, and sparse sampling within a finite volume, using mock catalogs that mimic in detail the Mark III catalog and the dynamics of our cosmological neighborhood. The mock catalogs are also used for error analysis. The value of the mass PS at k = 0.1 \\ihmpc is (4.6 \\pm 1.4) \\times 10^3 \\Omega^{-1.2} \\3hmpc, and the local logarithmic slope is -1.45 \\pm 0.5. This translates to \\sigma_8 \\Omega^{0.6} \\simeq 0.7-0.8, depending on where the PS peak is. Direct comparisons of the mass PS with the galaxy PS derived from different redshift and angular survey...
Spectrum management considerations of adaptive power control in satellite networks
Sawitz, P.; Sullivan, T.
1983-01-01
Adaptive power control concepts for the compensation of rain attenuation are considered for uplinks and downlinks. The performance of example power-controlled and fixed-EIRP uplinks is compared in terms of C/Ns and C/Is. Provisional conclusions are drawn with regard to the efficacy of uplink and downlink power control orbit/spectrum utilization efficiency.
Minimally Parametric Constraints on the Primordial Power Spectrum from Lyman-alpha
Bird, Simeon
2010-01-01
Current analyses of the Lyman-alpha forest assume that the primordial power spectrum of density perturbations obeys a simple power law, a strong theoretical assumption which should be tested. Employing a large suite of numerical simulations which drop this assumption, we reconstruct the shape of the primordial power spectrum using Lyman-alpha data from the Sloan Digital Sky Survey (SDSS). Our method combines a minimally parametric framework with cross-validation, a technique used to avoid over-fitting the data. Future work will involve predictions for the upcoming Baryon Oscillation Sky Survey (BOSS), which will provide new Lyman-alpha data with vastly decreased statistical errors.
Power spectrum with auxiliary fields in de Sitter space
Energy Technology Data Exchange (ETDEWEB)
Mohsenzadeh, M. [Islamic Azad University, Department of Physics, Qom Branch, Qom (Iran, Islamic Republic of); Tanhayi, M.R. [Islamic Azad University, Department of Physics, Central Tehran Branch, Tehran (Iran, Islamic Republic of); Yusofi, E. [Islamic Azad University, Department of Physics, Science and Research Ayatollah Amoli Branch, Amol, Mazandaran (Iran, Islamic Republic of)
2014-06-15
We use the auxiliary fields and (excited-) de Sitter solutions to study the standard power spectrum of primordial fluctuations of a scalar field in the early universe. The auxiliary fields are the negative norm solutions of the field equation and as is shown, with a fixed boundary condition, utilizing these states results in a finite power spectrum without any infinity. The power spectrum is determined by the de Sitter solutions up to some corrections and the space-time symmetry is not broken in this point of view. The modulation to the power spectrum is of order ((H)/(Λ)){sup 2}, where H is the Hubble parameter and Λ is the energy scale, e.g., the Planck scale. (orig.)
A New Exactly Solvable Inflation Model and its Power Spectrum
Institute of Scientific and Technical Information of China (English)
李新洲; 刘道军; 郝建纲
2003-01-01
We present a new exactly solvable inflation model in which inflation can stop automatically, and in the approximately de Sitter limit, we give its power spectrum which can be tested in the future observations of cosmic microwave background anisotropy.
Noncommutative geometry and the primordial dipolar imaginary power spectrum
Energy Technology Data Exchange (ETDEWEB)
Jain, Pankaj; Rath, Pranati K. [Indian Institue of Technology Kanpur, Department of Physics, Kanpur (India)
2015-03-01
We argue that noncommutative space-times lead to an anisotropic dipolar imaginary primordial power spectrum. We define a new product rule, which allows us to consistently extract the power spectrum in such space-times. The precise nature of the power spectrum depends on the model of noncommutative geometry. We assume a simple dipolar model which has a power dependence on the wave number, k, with a spectral index, α. We show that such a spectrum provides a good description of the observed dipole modulation in the cosmic microwave background radiation (CMBR) data with α ∼ 0. We extract the parameters of this model from the data. The dipole modulation is related to the observed hemispherical anisotropy in the CMBR data, which might represent the first signature of quantum gravity. (orig.)
Noncommutative geometry and the primordial dipolar imaginary power spectrum
Jain, Pankaj; Rath, Pranati K.
2015-03-01
We argue that noncommutative space-times lead to an anisotropic dipolar imaginary primordial power spectrum. We define a new product rule, which allows us to consistently extract the power spectrum in such space-times. The precise nature of the power spectrum depends on the model of noncommutative geometry. We assume a simple dipolar model which has a power dependence on the wave number, , with a spectral index, . We show that such a spectrum provides a good description of the observed dipole modulation in the cosmic microwave background radiation (CMBR) data with . We extract the parameters of this model from the data. The dipole modulation is related to the observed hemispherical anisotropy in the CMBR data, which might represent the first signature of quantum gravity.
MEASURING THE JET POWER OF FLAT-SPECTRUM RADIO QUASARS
Energy Technology Data Exchange (ETDEWEB)
Shabala, S. S.; Santoso, J. S. [School of Mathematics and Physics, University of Tasmania, Private Bag 37, Hobart, TAS 7001 (Australia); Godfrey, L. E. H. [International Centre for Radio Astronomy Research, Curtin University, GPO Box U1987, Perth, Western Australia 6845 (Australia)
2012-09-10
We use frequency-dependent position shifts of flat-spectrum radio cores to estimate the kinetic power of active galactic nucleus (AGN) jets. We find a correlation between the derived jet powers and AGN narrow-line luminosity, consistent with the well-known relation for radio galaxies and steep spectrum quasars. This technique can be applied to intrinsically weak jets even at high redshift.
The matter power spectrum from the Ly alpha forest : an optical depth estimate
Zaroubi, S; Nusser, A; Haehnelt, M; Kim, TS; Viel, M.
2006-01-01
We measure the matter power spectrum from 31 Ly alpha spectra spanning the redshift range of 1.6-3.6. The optical depth, tau, for Ly alpha absorption of the intergalactic medium is obtained from the flux using the inversion method of Nusser & Haehnelt. The optical depth is converted to density by us
Power Spectral Density Conversions and Nonlinear Dynamics
Directory of Open Access Journals (Sweden)
Mostafa Rassaian
1994-01-01
Full Text Available To predict the vibration environment of a payload carried by a ground or air transporter, mathematical models are required from which a transfer function to a prescribed input can be calculated. For sensitive payloads these models typically include linear shock isolation system stiffness and damping elements relying on the assumption that the isolation system has a predetermined characteristic frequency and damping ratio independent of excitation magnitude. In order to achieve a practical spectral analysis method, the nonlinear system has to be linearized when the input transportation and handling vibration environment is in the form of an acceleration power spectral density. Test data from commercial isolators show that when nonlinear stiffness and damping effects exist the level of vibration input causes a variation in isolator resonant frequency. This phenomenon, described by the stationary response of the Duffing oscillator to narrow-band Gaussian random excitation, requires an alternative approach for calculation of power spectral density acceleration response at a shock isolated payload under random vibration. This article details the development of a plausible alternative approach for analyzing the spectral response of a nonlinear system subject to random Gaussian excitations.
1/f noise in music and speech. [Power spectrum studies
Energy Technology Data Exchange (ETDEWEB)
Voss, R.F.; Clarke, J.
1975-11-27
The power spectrum, S(f), of many fluctuating physical variables, V(t), is approximately ''1/f-like.'' Loudness fluctuations in music and speech and pitch (melody) fluctuations in music were found to exhibit 1/f power spectra. This observation has implications for stochastic music composition. 3 figures. (RWR)
47 CFR 25.208 - Power flux density limits.
2010-10-01
... Region 2, the single-entry equivalent power-flux density, in the space-to-Earth direction, (EPFDdown), at... in Region 1 and 12.2-12.7 GHz in Region 2, the aggregate equivalent power-flux density, in the space... power flux density levels defined below. (1) In the region of the contiguous United States,...
Energy Technology Data Exchange (ETDEWEB)
Heitmann, Katrin [Los Alamos National Laboratory; Habib, Salman [Los Alamos National Laboratory; Higdon, David [Los Alamos National Laboratory; Williams, Brian J [Los Alamos National Laboratory; White, Martin [Los Alamos National Laboratory; Wagner, Christian [Los Alamos National Laboratory
2008-01-01
The power spectrum of density fluctuations is a foundational source of cosmological information. Precision cosmological probes targeted primarily at investigations of dark energy require accurate theoretical determinations of the power spectrum in the nonlinear regime. To exploit the observational power of future cosmological surveys, accuracy demands on the theory are at the one percent level or better. Numerical simulations are currently the only way to produce sufficiently error-controlled predictions for the power spectrum. The very high computational cost of (precision) N-body simulations is a major obstacle to obtaining predictions in the nonlinear regime, while scanning over cosmological parameters. Near-future observations, however, are likely to provide a meaningful constraint only on constant dark energy equation of state 'wCDM' cosmologies. In this paper we demonstrate that a limited set of only 37 cosmological models -- the 'Coyote Universe' suite -- can be used to predict the nonlinear matter power spectrum at the required accuracy over a prior parameter range set by cosmic microwave background observations. This paper is the second in a series of three, with the final aim to provide a high-accuracy prediction scheme for the nonlinear matter power spectrum for wCDM cosmologies.
Cosmological power spectrum in a noncommutative spacetime
Kothari, Rahul; Rath, Pranati K.; Jain, Pankaj
2016-09-01
We propose a generalized star product that deviates from the standard one when the fields are considered at different spacetime points by introducing a form factor in the standard star product. We also introduce a recursive definition by which we calculate the explicit form of the generalized star product at any number of spacetime points. We show that our generalized star product is associative and cyclic at linear order. As a special case, we demonstrate that our recursive approach can be used to prove the associativity of standard star products for same or different spacetime points. The introduction of a form factor has no effect on the standard Lagrangian density in a noncommutative spacetime because it reduces to the standard star product when spacetime points become the same. We show that the generalized star product leads to physically consistent results and can fit the observed data on hemispherical anisotropy in the cosmic microwave background radiation.
Modeling the Void H I Column Density Spectrum
Manning, C V
2003-01-01
The equivalent width distribution function (EWDF) of \\hone absorbers specific to the void environment has been recently derived (Manning 2002), revealing a large line density of clouds (dN/dz ~500 per unit z for Log (N_HI)> 12.4). I show that the void absorbers cannot be diffuse (or so-called filamentary) clouds, expanding with the Hubble flow, as suggested by N-body/hydro simulations. Absorbers are here modeled as the baryonic remnants of sub-galactic perturbations that have expanded away from their dark halos in response to reionization at z ~ 6.5. A 1-D Lagrangian hydro/gravity code is used to follow the dynamic evolution and ionization structure of the baryonic clouds for a range of halo circular velocities. The simulation products at z=0 can be combined according to various models of the halo velocity distribution function to form a column density spectrum that can be compared with the observed. I find that such clouds may explain the observed EWDF if the halo velocity distribution function is as steep a...
Statistics of the Sunyaev-Zel'dovich Effect power spectrum
Peel, Michael W; Kay, Scott T
2009-01-01
Using large numbers of simulations of the microwave sky, incorporating the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich (SZ) effect due to clusters, we investigate the statistics of the power spectrum at microwave frequencies between spherical multipoles of 1000 and 10000. From these virtual sky maps, we find that the spectrum of the SZ effect has a larger standard deviation by a factor of 3 than would be expected from purely Gaussian realizations, and has a distribution that is significantly skewed towards higher values, especially when small map sizes are used. The standard deviation is also increased by around 10 percent compared to the trispectrum calculation due to the clustering of galaxy clusters. We also consider the effects of including residual point sources and uncertainties in the gas physics. This has implications for the excess power measured in the CMB power spectrum by the Cosmic Background Imager and BIMA experiments. Our results indicate that the observed excess could be expl...
Energy Technology Data Exchange (ETDEWEB)
Chluba, Jens; Erickcek, Adrienne L.; Ben-Dayan, Ido, E-mail: jchluba@cita.utoronto.ca [Canadian Institute for Theoretical Astrophysics, 60 St. George Street, Toronto, Ontario M5S 3H8 (Canada)
2012-10-20
In the early universe, energy stored in small-scale density perturbations is quickly dissipated by Silk damping, a process that inevitably generates {mu}- and y-type spectral distortions of the cosmic microwave background (CMB). These spectral distortions depend on the shape and amplitude of the primordial power spectrum at wavenumbers k {approx}< 10{sup 4} Mpc{sup -1}. Here, we study constraints on the primordial power spectrum derived from COBE/FIRAS and forecasted for PIXIE. We show that measurements of {mu} and y impose strong bounds on the integrated small-scale power, and we demonstrate how to compute these constraints using k-space window functions that account for the effects of thermalization and dissipation physics. We show that COBE/FIRAS places a robust upper limit on the amplitude of the small-scale power spectrum. This limit is about three orders of magnitude stronger than the one derived from primordial black holes in the same scale range. Furthermore, this limit could be improved by another three orders of magnitude with PIXIE, potentially opening up a new window to early universe physics. To illustrate the power of these constraints, we consider several generic models for the small-scale power spectrum predicted by different inflation scenarios, including running-mass inflation models and inflation scenarios with episodes of particle production. PIXIE could place very tight constraints on these scenarios, potentially even ruling out running-mass inflation models if no distortion is detected. We also show that inflation models with sub-Planckian field excursion that generate detectable tensor perturbations should simultaneously produce a large CMB spectral distortion, a link that could potentially be established with PIXIE.
Power Spectrum Estimation of Randomly Sampled Signals
DEFF Research Database (Denmark)
Velte, C. M.; Buchhave, P.; K. George, W.
The random, but velocity dependent, sampling of the LDA presents non-trivial signal processing challenges due to the high velocity bias and the arbitrariness of particle path through the measuring volume, among other factors. To obtain the desired non-biased statistics, it has previously been shown...... is that if the algorithms are not able to produce correct statistics from this simple signal, then they will certainly not be able to function well for a more complex measured LDA signal. This is, of course, true also for other methods that are based on the tested algorithms. The extremes are tested by increasing, e....... Residence time weighting provides non-biased estimates regardless of setting. The free-running processor was also tested and compared to residence time weighting using actual LDA measurements in a turbulent round jet. Power spectra from measurements on the jet centerline and the outer part of the jet...
Testing for New Physics: Neutrinos and the Primordial Power Spectrum
Canac, Nicolas; Abazajian, Kevork N; Easther, Richard; Price, Layne C
2016-01-01
We test the sensitivity of neutrino parameter constraints from combinations of CMB and LSS data sets to the assumed form of the primordial power spectrum (PPS) using Bayesian model selection. Significantly, none of the tested combinations, including recent high-precision local measurements of $\\mathrm{H}_0$ and cluster abundances, indicate a signal for massive neutrinos or extra relativistic degrees of freedom. For PPS models with a large, but fixed number of degrees of freedom, neutrino parameter constraints do not change significantly if the location of any features in the PPS are allowed to vary, although neutrino constraints are more sensitive to PPS features if they are known a priori to exist at fixed intervals in $\\log k$. Although there is no support for a non-standard neutrino sector from constraints on both neutrino mass and relativistic energy density, we see surprisingly strong evidence for features in the PPS when it is constrained with data from Planck 2015, SZ cluster counts, and recent high-pr...
A neutrino model fit to the CMB power spectrum
Shanks, T.; Johnson, R. W. F.; Schewtschenko, J. A.; Whitbourn, J. R.
2014-12-01
The standard cosmological model, Λ cold dark matter (ΛCDM), provides an excellent fit to cosmic microwave background (CMB) data. However, the model has well-known problems. For example, the cosmological constant, Λ, is fine-tuned to 1 part in 10100 and the CDM particle is not yet detected in the laboratory. Shanks previously investigated a model which assumed neither exotic particles nor a cosmological constant but instead postulated a low Hubble constant (H0) to allow a baryon density compatible with inflation and zero spatial curvature. However, recent Planck results make it more difficult to reconcile such a model with CMB power spectra. Here, we relax the previous assumptions to assess the effects of assuming three active neutrinos of mass ≈5 eV. If we assume a low H0 ≈ 45 km s-1 Mpc-1 then, compared to the previous purely baryonic model, we find a significantly improved fit to the first three peaks of the Planck power spectrum. Nevertheless, the goodness of fit is still significantly worse than for ΛCDM and would require appeal to unknown systematic effects for the fit ever to be considered acceptable. A further serious problem is that the amplitude of fluctuations is low (σ8 ≈ 0.2), making it difficult to form galaxies by the present day. This might then require seeds, perhaps from a primordial magnetic field, to be invoked for galaxy formation. These and other problems demonstrate the difficulties faced by models other than ΛCDM in fitting ever more precise cosmological data.
The X-ray variability of NGC 6814 - Power spectrum
Done, C.; Madejski, G. M.; Mushotzky, R. F.; Turner, T. J.; Koyama, K.; Kunieda, H.
1992-01-01
The existence of the periodic component seen in NGC 6814 with Exosat at 12,000 +/- 100 s is confirmed by a power spectrum and folded light curve analysis of unevenly sampled Ginga data. A comparison of the power spectra produced from simulated light curves with that observed enables the intrinsic shape of the power spectrum of the source to be determined despite the distortions introduced by the window function. The best estimate for the period is 12,132 +/- 3 s, where the error is that derived from simulations. An upper limit to the rate of change of period of about 10 exp -9 is inferred if the light curves are truly phase-coherent, but as this is not required by the data, the conservative upper limit is not greater than 5 x 10 exp -7. The large amount of power in the periodic component and its stability both suggest occultation of the source as its origin.
Energy Technology Data Exchange (ETDEWEB)
Chen Lingen E-mail: lgchenna@public.wh.hb.cn; Zheng Junlin; Sun Fengrui; Wu Chih
2003-09-01
The performance of a closed cycle helium turbine nuclear power plant for submarine propulsion is optimized in this paper. The power output, power density (ratio of power output to maximum specific volume in the cycle) and thermal efficiency of the cycle are derived. The maximum power, power density and efficiency are obtained by searching for the optimum heat conductance distribution among the hot side heat exchanger (intermediate heat exchanger), cold side heat exchanger (precooler) and recuperator for fixed total heat exchanger inventory with respect to the corresponding optimization objectives. The optimum results are compared with those reported in recent references for the conceptual design of a closed cycle helium turbine nuclear power plant for submarine propulsion. The numerical example shows that the method herein is valid and effective.
Massive Neutrinos and the Non-linear Matter Power Spectrum
Bird, Simeon; Haehnelt, Martin G
2011-01-01
We perform an extensive suite of N-body simulations of the matter power spectrum, incorporating massive neutrinos in the range M = 0.15-0.6 eV, probing the non-linear regime at scales k < 10 hMpc-1 at z < 3. We extend the widely used HALOFIT approximation (Smith et al. 2003) to account for the effect of massive neutrinos on the power spectrum. In the strongly non-linear regime HALOFIT systematically over-predicts the suppression due to the free-streaming of the neutrinos. The maximal discrepancy occurs at k \\sim 1hMpc-1, and is at the level of 10% of the total suppression. Most published constraints on neutrino masses based on HALOFIT are not affected, as they rely on data probing the matter power spectrum in the linear or mildly non-linear regime. However, predictions for future galaxy, Lyman-alpha forest and weak lensing surveys extending to more non-linear scales will benefit from the improved approximation to the non-linear matter power spectrum we provide. Our approximation reproduces the induced n...
Measurement of output power density from mobile phone as a function of input sound frequency.
Calabrò, Emanuele; Magazù, Salvatore
2013-01-01
Measurements of power density emitted by a mobile phone were carried out as a function of the sound frequency transmitted by a sound generator, ranging from 250 to 14000 Hz. Output power density was monitored by means of the selective radiation meter Narda SRM 3000 in spectrum analysis mode, and the octave frequency analysis of each tone used for the experimental design was acquired by the sound level meter Larson Davis LxT Wind. Vodafone providers were used for mobile phone calls with respect to various local base station in Southern-Italy. A relationship between the mobile phone microwaves power density and the sound frequencies transmitted by the sound generator was observed. In particular, microwaves power density level decreases significantly at sound frequency values larger than 4500 Hz. This result can be explained assuming that discontinuous transmission mode of global system for mobile communications is powered not only in silence-mode, but also at frequencies larger than 4500 Hz.
An Assessment of the Information Content of the Power Spectrum and Bispectrum
Chan, Kwan Chuen
2016-01-01
We study the covariance matrix of the power spectrum and bispectrum for dark matter and halos. Using a large suite of simulations from the DEUS-PUR project, we find that the non-Gaussian contributions to the covariance of the power spectrum and bispectrum are significant for both dark matter and halos already at the mildly nonlinear scales. We compute the leading disconnected non-Gaussian correction to the matter bispectrum covariance, and find that the predictions improve the agreement in the mildly nonlinear regime. The shot noise contributions to the covariance of the halo power spectrum and bispectrum are computed. When the ensemble averaged number density is used, the Poisson model covariances are in decent agreement with the measurements. When the number density is estimated and subtracted from each realization, the covariances are significantly reduced and get close to the Gaussian ones. The signal-to-noise ratio, S/N of the halo power spectrum levels off in the mildly nonlinear regime, $k \\sim 0.1 - 0...
Unbiased pseudo-Cl power spectrum estimation with mode projection
Elsner, Franz; Peiris, Hiranya V
2016-01-01
With the steadily improving sensitivity afforded by current and future galaxy surveys, a robust extraction of two-point correlation function measurements may become increasingly hampered by the presence of astrophysical foregrounds or observational systematics. The concept of mode projection has been introduced as a means to remove contaminants for which it is possible to construct a spatial map reflecting the expected signal contribution. Owing to its computational efficiency compared to minimum-variance methods, the sub-optimal pseudo-Cl (PCL) power spectrum estimator is a popular tool for the analysis of high-resolution data sets. Here, we integrate mode projection into the framework of PCL power spectrum estimation. In contrast to results obtained with optimal estimators, we show that the uncorrected projection of template maps leads to biased power spectra. Based on analytical calculations, we find exact closed-form expressions for the expectation value of the bias and demonstrate that they can be recast...
Reconstructing the spectrum of the pregalactic density field from astronomical data
Kashlinsky, A
1998-01-01
In this paper we evaluate the spectrum of the pregalactic density field on scales $1h^{-1}Mpc < r < 100h^{-1}$Mpc from a variety of astronomical data. APM data on $w(\\theta)$ in six narrow magnitude is used, after correcting to possible evolutionary effects, to constrain the spectrum of galaxy clustering on scales $10h^{-1}Mpc < r < 50-100h^{-1}Mpc$. Fitting power spectra of CDM models to the data at all depths requires $\\Omega h=0.2$ if the primordial index $n=1$ and $\\Omega h=0.3$ if the spectrum is tilted with $n=0.7$. Then we compare the peculiar velocity field predicted by the APM spectrum of galaxy (light) distribution with the actual velocity data. The two fields are consistent and the comparison suggests that the bias factor is scale independent with $\\Omega^{0.6}/b\\simeq$(0.2-0.3). The next dataset used comes from the cluster correlation data. We calculate in detail the amplification of the cluster correlation function due to gravitational clustering and use the data on both the slope of ...
Constraining the primordial power spectrum from SNIa lensing dispersion
Energy Technology Data Exchange (ETDEWEB)
Ben-Dayan, Ido [Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Kalaydzhyan, Tigran [State Univ. of New York, Stony Brook, NY (United States). Dept. of Physics and Astronomy
2013-09-15
The (absence of detecting) lensing dispersion of Supernovae type Ia (SNIa) can be used as a novel and extremely efficient probe of cosmology. In this preliminary example we analyze its consequences for the primordial power spectrum. The main setback is the knowledge of the power spectrum in the non-linear regime, 1 Mpc{sup -1}
Polymerization contraction of resin composite vs. energy and power density of light-cure.
Asmussen, Erik; Peutzfeldt, Anne
2005-10-01
This study measured the polymerization contraction of a resin composite cured at three levels of energy density, each attained at six different levels of power density. The polymerization contraction of the composite was recorded by the method of the deflecting disc (n = 5) for 1 h following the start of irradiation. Power densities of 50, 100, 200, 400, 800 and 1,000 mW cm(-2), as measured on a dental radiometer, were obtained by variation of distance and supply voltage of a commercial light-curing unit. The spectral distribution at each power density was recorded using a spectrophotometer. The absorption spectrum of camphorquinone was also recorded, and the efficiency of the radiation at each power density was calculated as the integral over wavelength of the product of absorption and emission. From the slope of the contraction curves, an approximation to the initial rate of polymerization, Rp, was calculated and was taken as an alternative measure of power density. Statistical analyses showed that polymerization contraction increased significantly with increasing levels of energy density received by the resin composite, and, for each level of energy density, that the contraction decreased significantly with increasing power density.
High Energy Density Capacitors for Pulsed Power Applications
2009-07-01
high energy density energy storage capacitors. High efficency capacitors are available with energy densities as high as 3 J/cc for 1000 shots or...GENERAL ATOMICS ENERGY PRODUCTS Engineering Bulletin HIGH ENERGY DENSITY CAPACITORS FOR PULSED POWER APPLICATIONS Fred MacDougall, Joel...00-2009 4. TITLE AND SUBTITLE High Energy Density Capacitors for Pulsed Power Applications 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM
Cosmic microwave background power spectrum estimation with the destriping technique
Poutanen, T.; Maino, D.; Kurki-Suonio, H.; Keihänen, E.; Hivon, E.
2004-09-01
Extraction of the cosmic microwave background (CMB) angular power spectrum is a challenging task for current and future CMB experiments due to the large data sets involved. Here we describe an implementation of Monte Carlo apodized spherical transform estimator (MASTER) described in Hivon et al., which exploits the destriping technique as a map-making method. In this method a noise estimate based on destriped noise-only Monte Carlo (MC) simulations is subtracted from the pseudo-angular power spectrum. As a working case we use realistic simulations of the Planck low-frequency instrument (LFI). We found that the effect of destriping on a pure sky signal is minimal and requires no correction. Instead we found an effect related to the distribution of detector pointings, which affects the high-l part of the power spectrum. We correct for this by subtracting a `signal bias' estimated by MC simulations. We also give analytical estimates for this signal bias. Our method is fast and accurate enough (the estimator is unbiased and errors are close to theoretical expectations for maximal accuracy) to estimate the CMB angular power spectra for current and future CMB space missions. This study is related to Planck LFI activities.
Chluba, Jens; Erickcek, Adrienne L.; Ben-Dayan, Ido
2012-10-01
In the early universe, energy stored in small-scale density perturbations is quickly dissipated by Silk damping, a process that inevitably generates μ- and y-type spectral distortions of the cosmic microwave background (CMB). These spectral distortions depend on the shape and amplitude of the primordial power spectrum at wavenumbers k FIRAS and forecasted for PIXIE. We show that measurements of μ and y impose strong bounds on the integrated small-scale power, and we demonstrate how to compute these constraints using k-space window functions that account for the effects of thermalization and dissipation physics. We show that COBE/FIRAS places a robust upper limit on the amplitude of the small-scale power spectrum. This limit is about three orders of magnitude stronger than the one derived from primordial black holes in the same scale range. Furthermore, this limit could be improved by another three orders of magnitude with PIXIE, potentially opening up a new window to early universe physics. To illustrate the power of these constraints, we consider several generic models for the small-scale power spectrum predicted by different inflation scenarios, including running-mass inflation models and inflation scenarios with episodes of particle production. PIXIE could place very tight constraints on these scenarios, potentially even ruling out running-mass inflation models if no distortion is detected. We also show that inflation models with sub-Planckian field excursion that generate detectable tensor perturbations should simultaneously produce a large CMB spectral distortion, a link that could potentially be established with PIXIE.
Estimating magnetic field power spectrum using CRRES magnetometer data
Ali, A.; Elkington, S. R.
2013-05-01
Radial diffusion is one of the acceleration mechanisms responsible for populating and depleting the Van Allen radiation belts with high energy charged particles. We use the magnetometer data from the Combined Release and Radiation Effects Satellite (CRRES) to estimate the power spectral density in the compressional component of the geomagnetic field in the frequency range of 0.8mHz-16.3mHz. We see a clear dependence of power spectral density on radial distance L, measure of geomagnetic disturbance Kp, and magnetic local time. Comparing total integrated power, the noon sector contains more power with no significant difference between other sectors during periods of low activity. During high activity the dusk sector has significantly more power than dawn sector with the difference sometimes being an order of magnitude higher with power increasing slightly as we move radially outward to higher L-shells. We then recompute the power spectral density without local time dependence and compute the electromagnetic part of the radial diffusion coefficient. The electromagnetic diffusion coefficients are then compared with the electrostatic coefficients computed by Brautigam et al. (2005). The dependence of the diffusion coefficients is then studied on parameters of L, Kp, and the first invariant. For a fixed first invariant the diffusion coefficient can be up to two orders of magnitude higher as we move from the inner magnetosphere (L=3.5) to the outer magnetosphere (L=6.5). During high activity, radial diffusion is also significantly faster than at quiet times.
Baryon Acoustic Oscillations in 2D: Modeling Redshift-space Power Spectrum from Perturbation Theory
Taruya, Atsushi; Saito, Shun
2010-01-01
We present an improved prescription for matter power spectrum in redshift space taking a proper account of both the non-linear gravitational clustering and redshift distortion, which are of particular importance for accurately modeling baryon acoustic oscillations (BAOs). Contrary to the models of redshift distortion phenomenologically introduced but frequently used in the literature, the new model includes the corrections arising from the non-linear coupling between the density and velocity fields associated with two competitive effects of redshift distortion, i.e., Kaiser and Finger-of-God effects. Based on the improved treatment of perturbation theory for gravitational clustering, we compare our model predictions with monopole and quadrupole power spectra of N-body simulations, and an excellent agreement is achieved over the scales of BAOs. Potential impacts on constraining dark energy and modified gravity from the redshift-space power spectrum are also investigated based on the Fisher-matrix formalism. We...
On Removing Interloper Contamination from Intensity Mapping Power Spectrum Measurements
Lidz, Adam
2016-01-01
Line intensity mapping experiments seek to trace large scale structure by measuring the spatial fluctuations in the combined emission, in some convenient spectral line, from individually unresolved galaxies. An important systematic concern for these surveys is line confusion from foreground or background galaxies emitting in other lines that happen to lie at the same observed frequency as the "target" emission line of interest. We develop an approach to separate this "interloper" emission at the power spectrum level. If one adopts the redshift of the target emission line in mapping from observed frequency and angle on the sky to co-moving units, the interloper emission is mapped to the wrong co-moving coordinates. Since the mapping is different in the line of sight and transverse directions, the interloper contribution to the power spectrum becomes anisotropic, especially if the interloper and target emission are at widely separated redshifts. This distortion is analogous to the Alcock-Paczynski test, but her...
Unbiased contaminant removal for 3D galaxy power spectrum measurements
Kalus, Benedict; Bacon, David; Samushia, Lado
2016-01-01
We assess and develop techniques to remove contaminants when calculating the 3D galaxy power spectrum. We separate the process into three separate stages: (i) removing the contaminant signal, (ii) estimating the uncontaminated cosmological power spectrum, (iii) debiasing the resulting estimates. For (i), we show that removing the best-fit contaminant (template subtraction), and setting the contaminated components of the covariance to be infinite (mode deprojection) are mathematically equivalent. For (ii), performing a Quadratic Maximum Likelihood (QML) estimate after mode deprojection gives an optimal unbiased solution, although it requires the manipulation of large $(N_{\\rm mode}^2)$ matrices, which is unfeasible for recent 3D galaxy surveys. Measuring a binned average of the modes for (ii) as proposed by Feldman, Kaiser & Peacock (1994, FKP) is faster and simpler, but is sub-optimal and gives rise to a biased solution. We present a method to debias the resulting FKP measurements that does not require an...
Multiple Cosmic Collisions and the Microwave Background Power Spectrum
Kozaczuk, Jonathan
2012-01-01
Collisions between cosmic bubbles of different vacua are a generic feature of false vacuum eternal inflation scenarios. While previous studies have focused on the consequences of a single collision event in an observer's past, we begin here an investigation of the more general scenario allowing for many "mild" collisions intersecting our past light cone (and one another). We discuss the general features of multiple collision scenarios and consider their impact on the cosmic microwave background (CMB) temperature power spectrum, treating the collisions perturbatively. In a large class of models, one can approximate a multiple collision scenario as a superposition of individual collision events governed by nearly isotropic and scale-invariant distributions, most appearing to take up less than half of the sky. In this case, the shape of the expected CMB temperature spectrum maintains statistical isotropy and typically features a dramatic increase in power in the low multipoles relative to that of the best-fit $\\...
Cosmological parameter estimation with free-form primordial power spectrum
Hazra, Dhiraj Kumar; Souradeep, Tarun
2013-01-01
Constraints on the main cosmological parameters using CMB or large scale structure data are usually based on power-law assumption of the primordial power spectrum (PPS). However, in the absence of a preferred model for the early universe, this raises a concern that current cosmological parameter estimates are strongly prejudiced by the assumed power-law form of PPS. In this paper, for the first time, we perform cosmological parameter estimation allowing the free form of the primordial spectrum. This is in fact the most general approach to estimate cosmological parameters without assuming any particular form for the primordial spectrum. We use direct reconstruction of the PPS for any point in the cosmological parameter space using recently modified Richardson-Lucy algorithm however other alternative reconstruction methods could be used for this purpose as well. We use WMAP 9 year data in our analysis considering CMB lensing effect and we report, for the first time, that the flat spatial universe with no cosmol...
Cosmic microwave background power spectrum estimation with the destriping technique
Poutanen, T; Kurki-Suonio, H; Keihanen, E; Hivon, E
2004-01-01
Extraction of the CMB (Cosmic Microwave Background) angular power spectrum is a challenging task for current and future CMB experiments due to the large data sets involved. Here we describe an implementation of MASTER (Monte carlo Apodised Spherical Transform EstimatoR) which exploits the destriping technique as a map-making method. In this method a noise estimate based on destriped noise-only MC (Monte Carlo) simulations is subtracted from the pseudo angular power spectrum. As a working case we use realistic simulations of the PLANCK LFI (Low Frequency Instrument). We found that the effect of destriping on a pure sky signal is minimal and requires no correction. Instead we found an effect related to the distribution of detector pointings, which affects the high multipole part of the power spectrum. We correct for this by subtracting a ``signal bias'' estimated by MC simulations. We also give analytical estimates for this signal bias. Our method is fast and accurate enough (the estimator is un-biased and erro...
Cosmological constraints from thermal Sunyaev Zeldovich power spectrum revisited
Horowitz, Benjamin
2016-01-01
Thermal Sunyaev-Zeldovich (tSZ) power spectrum is one of the most sensitive methods to constrain cosmological parameters, scaling as the amplitude $\\sigma_8^8$. It is determined by the integral over the halo mass function multiplied by the total pressure content of clusters, and further convolved by the cluster gas pressure profile. It has been shown that various feedback effects can change significantly the pressure profile, strongly affecting the tSZ power spectrum at high $l$. Energetics arguments and SZ-halo mass scaling relations suggest feedback is unlikely to significantly change the total pressure content, making low $l$ tSZ power spectrum more robust against feedback effects. Furthermore, the separation between the cosmic infrared background (CIB) and tSZ is more reliable at low $l$. Low $l$ modes are however probing very small volumes, giving rise to very large non-gaussian sampling variance errors. By computing the trispectrum contribution we identify $90
Measuring the power spectrum of dark matter substructure using strong gravitational lensing
Hezaveh, Yashar; Dalal, Neal; Holder, Gilbert; Kisner, Theodore; Kuhlen, Michael; Perreault Levasseur, Laurence
2016-11-01
In recent years, it has become possible to detect individual dark matter subhalos near images of strongly lensed extended background galaxies. Typically, only the most massive subhalos in the strong lensing region may be detected this way. In this work, we show that strong lenses may also be used to constrain the much more numerous population of lower mass subhalos that are too small to be detected individually. In particular, we show that the power spectrum of projected density fluctuations in galaxy halos can be measured using strong gravitational lensing. We develop the mathematical framework of power spectrum estimation, and test our method on mock observations. We use our results to determine the types of observations required to measure the substructure power spectrum with high significance. We predict that deep observations (~10 hours on a single target) with current facilities can measure this power spectrum at the 3σ level, with no apparent degeneracy with unknown clumpiness in the background source structure or fluctuations from detector noise. Upcoming ALMA measurements of strong lenses are capable of placing strong constraints on the abundance of dark matter subhalos and the underlying particle nature of dark matter.
Joint likelihood function of cluster number counts and weak lensing power spectrum
Takada, Masahiro
2013-01-01
A coherent over- or under-density contrast across a finite survey volume causes an upward- or downward- fluctuation in the number of halos. This fluctuation in halo number adds a significant co-variant scatter in the observed amplitudes of weak lensing power spectrum at nonlinear, small scales. Because of this covariance, the amount of information that can be extracted from a measurement of the weak lensing power spectrum is significantly smaller than naive estimates. In this paper, we show that by measuring both the number counts of clusters and the power spectrum in the same survey region, we can mitigate this loss of information and significantly enhance the scientific return from the upcoming surveys. First, using the halo model approach, we derive the joint likelihood function of the halo number counts and the weak lensing power spectrum, taking into account the super-sample co-variance effect on the two observables. We show that the analytical model matches the distributions measured from 1000 realizati...
Large-Scale Power Spectrum and Cosmological Parameters from SFI Peculiar Velocities
Freudling, W; Da Costa, L N; Dekel, A; Eldar, A; Giovanelli, R; Haynes, M P; Salzer, J J; Wegner, G; Zaroubi, S; Freudling, Wolfram; Zehavi, Idit; Costa, Luiz N. da; Dekel, Avishai; Eldar, Amiram; Giovanelli, Riccardo; Haynes, Martha P.; Salzer, John J.; Wegner, Gary; Zaroubi, Saleem
1999-01-01
We estimate the power spectrum of mass density fluctuations from peculiar velocities of galaxies by applying an improved maximum-likelihood technique to the new all-sky SFI catalog. Parametric models are used for the power spectrum and the errors, and the free parameters are determined by assuming Gaussian velocity fields and errors and maximizing the probability of the data given the model. It has been applied to generalized CDM models with and without COBE normalization. The method has been carefully tested using artificial SFI catalogs. The most likely distance errors are found to be similar to the original error estimates in the SFI data. The general result that is not very sensitive to the prior model used is a relatively high amplitude of the power spectrum. For example, at k=0.1 h/Mpc we find P(k)Ømega^{1.2}=(4.4+/-1.7)X10^3 (Mpc/h)^3. An integral over the power spectrum yields cosmological parameters are obtained for families of CDM models. For example, for COBE-normalized \\Lambda CDM models (scalar ...
H-ATLAS: THE COSMIC ABUNDANCE OF DUST FROM THE FAR-INFRARED BACKGROUND POWER SPECTRUM
Energy Technology Data Exchange (ETDEWEB)
Thacker, Cameron; Cooray, Asantha; Smidt, Joseph; De Bernardis, Francesco; Mitchell-Wynne, K. [Department of Physics and Astronomy, University of California, Irvine, CA 92697 (United States); Amblard, A. [NASA Ames Research Center, Moffett Field, CA 94035 (United States); Auld, R.; Eales, S.; Pascale, E. [School of Physics and Astronomy, Cardiff University, The Parade, Cardiff, CF24 3AA (United Kingdom); Baes, M.; Michalowski, M. J. [Sterrenkundig Observatorium, Universiteit Gent, KrijgslAAn 281 S9, B-9000 Gent (Belgium); Clements, D. L.; Dariush, A.; Hopwood, R. [Physics Department, Imperial College London, South Kensington campus, London, SW7 2AZ (United Kingdom); De Zotti, G. [INAF, Osservatorio Astronomico di Padova, Vicolo Osservatorio 5, I-35122 Padova (Italy); Dunne, L.; Maddox, S. [Department of Physics and Astronomy, University of Canterbury, Private Bag 4800, Christchurch (New Zealand); Hoyos, C. [School of Physics and Astronomy, University of Nottingham, University Park, Nottingham, NG7 2RD (United Kingdom); Ibar, E. [UK Astronomy Technology Centre, The Royal Observatory, Blackford Hill, Edinburgh, EH9 3HJ (United Kingdom); Jarvis, M. [Astrophysics, Department of Physics, Keble Road, Oxford, OX1 3RH (United Kingdom); and others
2013-05-01
We present a measurement of the angular power spectrum of the cosmic far-infrared background (CFIRB) anisotropies in one of the extragalactic fields of the Herschel Astrophysical Terahertz Large Area Survey at 250, 350, and 500 {mu}m bands. Consistent with recent measurements of the CFIRB power spectrum in Herschel-SPIRE maps, we confirm the existence of a clear one-halo term of galaxy clustering on arcminute angular scales with large-scale two-halo term of clustering at 30 arcmin to angular scales of a few degrees. The power spectrum at the largest angular scales, especially at 250 {mu}m, is contaminated by the Galactic cirrus. The angular power spectrum is modeled using a conditional luminosity function approach to describe the spatial distribution of unresolved galaxies that make up the bulk of the CFIRB. Integrating over the dusty galaxy population responsible for the background anisotropies, we find that the cosmic abundance of dust, relative to the critical density, to be between {Omega}{sub dust} = 10{sup -6} and 8 Multiplication-Sign 10{sup -6} in the redshift range z {approx} 0-3. This dust abundance is consistent with estimates of the dust content in the universe using quasar reddening and magnification measurements in the Sloan Digital Sky Survey.
The Power Spectrum of Ionic Nanopore Currents: The Role of Ion Correlations
Zorkot, Mira; Bonthuis, Douwe Jan
2015-01-01
We calculate the power spectrum of electric-field-driven ion transport through cylindrical nanometer-scale pores using both linearized mean-field theory and Langevin dynamics simulations. With the atom-sized cutoff radius as the only fitting parameter, the linearized mean-field theory accurately captures the dependence of the simulated power spectral density on the pore radius and the applied electric field. Remarkably, the linearized mean-field theory predicts a plateau in the power spectral density at low frequency ${\\omega}$, which is confirmed by the Langevin dynamics simulations at low ion concentration. At high ion concentration, however, the power spectral density follows a power law that is reminiscent of the $1/{\\omega}^{\\alpha}$ dependence found experimentally at low frequency. Based on simulations with and without ion-ion interactions, we attribute the low-frequency power law dependence to ion-ion correlations. Finally, we show that the surface charge density has no effect on the frequency dependen...
Einasto Profiles and the Dark Matter Power Spectrum
Ludlow, Aaron D
2016-01-01
We study the mass accretion histories (MAHs) and density profiles of dark matter halos using N-body simulations of self-similar gravitational clustering from scale-free power spectra, $P(k)\\propto k^n$. We pay particular attention to the density profile curvature, which we characterize using the shape parameter, $\\alpha$, of an Einasto profile. In agreement with previous findings our results suggest that, despite vast differences in their MAHs, the density profiles of virialized halos are remarkably alike. Nonetheless, clear departures from self-similarity are evident: for a given spectral index, $\\alpha$ increases slightly but systematically with "peak height", $\
Unbiased pseudo-Cℓ power spectrum estimation with mode projection
Elsner, Franz; Leistedt, Boris; Peiris, Hiranya V.
2017-02-01
With the steadily improving sensitivity afforded by current and future galaxy surveys, a robust extraction of two-point correlation function measurements may become increasingly hampered by the presence of astrophysical foregrounds or observational systematics. The concept of mode projection has been introduced as a means to remove contaminants for which it is possible to construct a spatial map, reflecting the expected signal contribution. Owing to its computational efficiency compared to minimum-variance methods, the sub-optimal pseudo-Cℓ (PCL) power spectrum estimator is a popular tool for the analysis of high-resolution data sets. Here, we integrate mode projection into the framework of PCL power spectrum estimation. In contrast to results obtained with optimal estimators, we show that the uncorrected projection of template maps leads to biased power spectra. Based on analytical calculations, we find exact closed-form expressions for the expectation value of the bias and demonstrate that they can be recast in a form which allows a numerically efficient evaluation, preserving the favourable O( ℓ_{max} ^3 ) time complexity of PCL estimator algorithms. Using simulated data sets, we assess the scaling of the bias with various analysis parameters and demonstrate that it can be reliably removed. We conclude that in combination with mode projection, PCL estimators allow for a fast and robust computation of power spectra in the presence of systematic effects - properties in high demand for the analysis of ongoing and future large-scale structure surveys.
High density operation for reactor-relevant power exhaust
Wischmeier, M.
2015-08-01
With increasing size of a tokamak device and associated fusion power gain an increasing power flux density towards the divertor needs to be handled. A solution for handling this power flux is crucial for a safe and economic operation. Using purely geometric arguments in an ITER-like divertor this power flux can be reduced by approximately a factor 100. Based on a conservative extrapolation of current technology for an integrated engineering approach to remove power deposited on plasma facing components a further reduction of the power flux density via volumetric processes in the plasma by up to a factor of 50 is required. Our current ability to interpret existing power exhaust scenarios using numerical transport codes is analyzed and an operational scenario as a potential solution for ITER like divertors under high density and highly radiating reactor-relevant conditions is presented. Alternative concepts for risk mitigation as well as strategies for moving forward are outlined.
The 44Ti-powered spectrum of SN 1987A
Jerkstrand, Anders; Kozma, Cecilia
2011-01-01
SN 1987A provides a unique opportunity to study the evolution of a supernova from explosion into very late phases. Due to the rich chemical structure, the multitude of physical process involved, and extensive radiative transfer effects, detailed modeling is needed to interpret the emission from this and other supernovae. In this paper, we analyze the late-time (~8 years) HST spectrum of the SN 1987A ejecta, where 44Ti is the dominant power source. Based on an explosion model for a 19 Msun progenitor, we compute a model spectrum by calculating the degradation of positrons and gamma-rays from the radioactive decays, solving the equations governing temperature, ionization balance and NLTE level populations, and treating the radiative transfer with a Monte Carlo technique. We obtain a UV/optical/NIR model spectrum which is found to reproduce most of the lines in the observed spectrum to good accuracy. We find non-local radiative transfer in atomic lines to be an important process also at this late stage of the su...
The ICM power spectrum: probing the gas physics of galaxy clusters
Gaspari, M.; Churazov, E.; Zhuravleva, I.; Lau, E.; Nagai, D.
2014-07-01
Exploring the power spectrum of fluctuations in the intracluster medium can deeply improve our knowledge of galaxy cluster physics, in analogy to what the cosmology field has experienced with CMB studies during the last decade. The normalization of the ICM spectrum (related to density, entropy, or pressure fluctuations) is linearly linked to the level of large-scale motions, which excite gravity and sound waves. The slope of the spectrum reflects instead the competition between the turbulence cascade and diffusive processes, which act to damp fluctuations and smooth the X-ray surface brightness images. Using high-resolution 3D plasma simulations in realistic galaxy clusters, we probe the behavior of the ICM power spectrum under different physics, such as turbulence and thermal conduction. We test our spectral modeling on deep X-ray observations of Coma cluster, retrieving mild subsonic turbulence and strongly suppressed conduction. Being able to probe the (astro)physics of the diffuse medium or, for instance, to easily retrieve the gas motions from the thermodynamic fluctuations, is a powerful tool with profound implications for the evolution of baryons in the universe, which can be exploited by the current (XMM-Newton, Chandra) and future (e.g. Astro-H, Athena+) generation of X-ray telescopes.
EEG Power Spectrum Analysis in Children with ADHD
Kamida, Akira; Shimabayashi, Kenta; Oguri, Masayoshi; Takamori, Toshihiro; Ueda, Naoyuki; Koyanagi, Yuki; Sannomiya, Naoko; Nagira, Haruki; Ikunishi, Saeko; Hattori, Yuiko; Sato, Kengo; Fukuda, Chisako; Hirooka, Yasuaki; Maegaki, Yoshihiro
2016-01-01
Background Attention deficit disorder/hyperactivity disorder (ADHD) is a pathological condition that is not fully understood. In this study, we investigated electroencephalographic (EEG) power differences between children with ADHD and healthy control children. Methods EEGs were recorded as part of routine medical care received by 80 children with ADHD aged 4–15 years at the Department of Pediatric Neurology in Tottori University Hospital. Additionally, we recorded in 59 control children aged 4–15 years after obtaining informed consent. Specifically, awake EEG signals were recorded from each child using the international 10–20 system, and we used ten 3-s epochs on the EEG power spectrum to calculate the powers of individual EEG frequency bands. Results The powers of different EEG bands were significantly higher in the frontal brain region of those in the ADHD group compared with the control group. In addition, the power of the beta band in the ADHD group was significantly higher in all brain regions, except for the occipital region, compared with control children. With regard to developmental changes, the power of the alpha band in the occipital region showed an age-dependent decrease in both groups, with slightly lower power in the ADHD group. Additionally, the intergroup difference decreased in children aged 11 years or older. As with the alpha band in the occipital region, the beta band in the frontal region showed an age-dependent decrease in both groups. Unlike the alpha band, the power of the beta band was higher in the ADHD group than in the control group for children of all ages. Conclusion The observed intergroup differences in EEG power may provide insight into the brain function of children with ADHD. PMID:27493489
Power Allocation for Balancing Spectrum Efficiency and Power Consumption in Cognitive Relay Networks
Directory of Open Access Journals (Sweden)
Lun Tang
2011-10-01
Full Text Available In order to guarantee the QoS requirement of secondary users and not to affect the outage probability of primary user in cognitive relay networks, we propose two optimal power allocation models: (1 maximizing the transmission rate of secondary users; (2 minimizing the total power consumption. Theory analysis shows that two optimal power allocation models conflict between spectrum efficiency and power consumption. Furthermore, an optimal power allocation model which joints the transmission rate and the total power consumption in cognitive relay networks is proposed. By using the Lagrangian method, the optimization algorithm for this model is designed. The proposed algorithm can achieve the trade-off between the transmission rate and the total power consumption by varying the weight. Simulation results show that the proposed algorithm can effectively adjust the transmission rate and the total power consumption of secondary users.
Power Spectrum Analysis of Three-Dimensional Redshift Surveys
Feldman, H A; Peacock, J A; Feldman, Hume A.; Kaiser, Nick; Peacock, John A.
1994-01-01
We develop a general method for power spectrum analysis of three dimensional redshift surveys. We present rigorous analytical estimates for the statistical uncertainty in the power and we are able to derive a rigorous optimal weighting scheme under the reasonable (and largely empirically verified) assumption that the long wavelength Fourier components are Gaussian distributed. We apply the formalism to the updated 1-in-6 QDOT IRAS redshift survey, and compare our results to data from other probes: APM angular correlations; the CfA and the Berkeley 1.2Jy IRAS redshift surveys. Our results bear out and further quantify the impression from e.g.\\ counts-in-cells analysis that there is extra power on large scales as compared to the standard CDM model with $\\Omega h\\simeq 0.5$. We apply likelihood analysis using the CDM spectrum with $\\Omega h$ as a free parameter as a phenomenological family of models; we find the best fitting parameters in redshift space and transform the results to real space. Finally, we calcul...
Improved Measurements of the CMB Power Spectrum with ACBAR
Kuo, C L; Bock, J J; Bond, J R; Contaldi, C R; Daub, M D; Goldstein, J H; Holzapfel, W L; Lange, A E; Lueker, M; Newcomb, M; Peterson, J B; Reichardt, C; Ruhl, J; Runyan, M C; Staniszweski, Z
2006-01-01
We report improved measurements of temperature anisotropies in the cosmic microwave background (CMB) radiation made with the Arcminute Cosmology Bolometer Array Receiver (ACBAR). In this paper, we use a new analysis technique and include 30% more data from the 2001 and 2002 observing seasons than the first release to derive a new set of band-power measurements with significantly smaller uncertainties. The planet-based calibration used previously has been replaced by comparing the flux of RCW38 as measured by ACBAR and BOOMERANG to transfer the WMAP-based BOOMERANG calibration to ACBAR. The resulting power spectrum is consistent with the theoretical predictions for a spatially flat, dark energy dominated LCDM cosmology including the effects of gravitational lensing. Despite the exponential damping on small angular scales, the primary CMB fluctuations are detected with a signal-to-noise ratio of greater than 4 up to multipoles of l=2000. This increase in the precision of the fine-scale CMB power spectrum leads ...
The 3D power spectrum of galaxies from the SDSS
Tegmark, M; Strauss, M; Hoyle, F; Schlegel, D J; Scoccimarro, R; Vogeley, M S; Weinberg, D H; Zehavi, I; Berlind, Andreas A; Budavari, T; Connolly, A; Eisenstein, D J; Finkbeiner, D; Frieman, J A; Gunn, J E; Hamilton, A J S; Hui, L; Jain, B; Johnston, D; Kent, S; Lin, H; Nakajima, R; Ostriker, J P; Nichol, R C; Pope, A; Scranton, R; Seljak, U; Sheth, R K; Stebbins, A; Szalay, A S; Szapudi, I; Verde, L; Xu, Y; Annis, J; Bahcall, Neta A; Brinkmann, J; Burles, S; Castander, F J; Csabai, I; Loveday, J; Doi, M; Fukugita, M; Gott, J R; Hennessy, G S; Hogg, D W; Ivezic, M E Z; Knapp, G R; Lamb, D Q; Lee Byung Cheol; Lupton, R H; McKay, T A; Kunszt, Peter Z; Munn, J A; O'Connell, L; Peoples, John; Pier, J R; Richmond, M; Rockosi, C M; Schneider, D P; Stoughton, C; Tucker, D L; Vanden Berk, Daniel E; Yanni, B; York, D G
2004-01-01
We measure the large-scale real-space power spectrum P(k) using a sample of 205,443 galaxies from the Sloan Digital Sky Survey, covering 2417 square degrees with mean redshift z~0.1. We employ a matrix-based method using pseudo-Karhunen-Loeve eigenmodes, producing uncorrelated minimum-variance measurements in 22 k-bands of both the clustering power and its anisotropy due to redshift-space distortions, with narrow and well-behaved window functions in the range 0.02 h/Mpc < k < 0.3h/Mpc. We pay particular attention to modeling, quantifying and correcting for potential systematic errors, nonlinear redshift distortions and the artificial red-tilt caused by luminosity-dependent bias. Our final result is a measurement of the real-space matter power spectrum P(k) up to an unknown overall multiplicative bias factor. Our calculations suggest that this bias factor is independent of scale to better than a few percent for k<0.1h/Mpc, thereby making our results useful for precision measurements of cosmological pa...
Viel, M; Viel, Matteo; Haehnelt, Martin G.
2006-01-01
(abridged) The flux power spectrum of the Lyman-alpha forest in quasar (QSO) absorption spectra is sensitive to a wide range of cosmological and astrophysical parameters and instrumental effects. Modelling the flux power spectrum in this large parameter space to an accuracy comparable to the statistical uncertainty of large samples of QSO spectra is very challenging. We use here a coarse grid of hydrodynamical simulations run with GADGET-2 to obtain a ``best guess'' model around which we calculate a finer grid of flux power spectra using a Taylor expansion of the flux power spectrum to first order. We find that the SDSS flux power spectrum alone is able to constrain a wide range of parameters including the amplitude of the matter power spectrum sigma_8, the matter density Omega_m, the spectral index of primordial density fluctuations n, the effective optical depth tau_eff and its evolution. The thermal history of the Intergalactic Medium (IGM) is, however, poorly constrained and the SDSS data favour either an...
Constraints on massive neutrinos from the CFHTLS angular power spectrum
Energy Technology Data Exchange (ETDEWEB)
Xia, Jun-Qing [Scuola Internazionale Superiore di Studi Avanzati, Via Bonomea 265, I-34136 Trieste (Italy); Granett, Benjamin R.; Guzzo, Luigi [INAF — Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Brera (Italy); Viel, Matteo [INAF — Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34131 Trieste (Italy); Bird, Simeon [School of Natural Sciences, Institute for Advanced Study, Princeton, NJ 08540 (United States); Haehnelt, Martin G. [Institute of Astronomy and Kavli Institute for Cosmology, Madingley Road, CB3 0HA, Cambridge (United Kingdom); Coupon, Jean [Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan (China); McCracken, Henry Joy; Mellier, Yannick, E-mail: xia@sissa.it, E-mail: ben.granett@brera.inaf.it, E-mail: viel@oats.inaf.it, E-mail: spb@ias.edu, E-mail: luigi.guzzo@brera.inaf.it, E-mail: haehnelt@ast.cam.ac.uk, E-mail: coupon@asiaa.sinica.edu.tw, E-mail: hjmcc@iap.fr, E-mail: mellier@iap.fr [Institut d' Astrophysique de Paris, UMR 7095 CNRS, Universitè Pierre et Marie Curie, 98 bis Boulevard Arago, 75014 Paris (France)
2012-06-01
We use the galaxy angular power spectrum at z ∼ 0.5–1.2 from the Canada-France-Hawaii-Telescope Legacy Survey Wide fields (CFHTLS-Wide) to constrain separately the total neutrino mass Σm{sub ν} and the effective number of neutrino species N{sub eff}. This survey has recently benefited from an accurate calibration of the redshift distribution, allowing new measurements of the (non-linear) matter power spectrum in a unique range of scales and redshifts sensitive to neutrino free streaming. Our analysis makes use of a recent model for the effect of neutrinos on the weakly non-linear matter power spectrum derived from accurate N-body simulations. We show that CFHTLS, combined with WMAP7 and a prior on the Hubble constant provides an upper limit of Σm{sub ν} < 0.29 eV and N{sub eff} = 4.17{sup +1.62}{sub −1.26} (2 σ confidence levels). If we omit smaller scales which may be affected by non-linearities, these constraints become Σm{sub ν} < 0.41 eV and N{sub eff} = 3.98{sup +2.02}{sub −1.20} (2 σ confidence levels). Finally we show that the addition of other large scale structures probes can further improve these constraints, demonstrating that high redshift large volumes surveys such as CFHTLS are complementary to other cosmological probes of the neutrino mass.
DEFF Research Database (Denmark)
Li, Qingnan; Andersen, Michael A. E.; Thomsen, Ole Cornelius
2011-01-01
Nowadays, efficiency and power density are the most important issues for Power Factor Correction (PFC) converters development. However, it is a challenge to reach both high efficiency and power density in a system at the same time. In this paper, taking a Bridgeless PFC (BPFC) as an example...
Primordial power spectrum of tensor perturbations in Finsler spacetime
Energy Technology Data Exchange (ETDEWEB)
Li, Xin [Chongqing University, Department of Physics, Chongqing (China); Chinese Academy of Sciences, State Key Laboratory Theoretical Physics, Institute of Theoretical Physics, Beijing (China); Wang, Sai [Chinese Academy of Sciences, State Key Laboratory Theoretical Physics, Institute of Theoretical Physics, Beijing (China)
2016-02-15
We first investigate the gravitational wave in the flat Finsler spacetime. In the Finslerian universe, we derive the perturbed gravitational field equation with tensor perturbations. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. Then we obtain the modified primordial power spectrum of the tensor perturbations. The parity violation feature requires that the anisotropic effect contributes to the TT, TE, EE, BB angular correlation coefficients with l{sup '} = l + 1 and TB, EB with l{sup '} = l. The numerical results show that the anisotropic contributions to the angular correlation coefficients depend on m, and TE and ET angular correlation coefficients are different. (orig.)
Primordial power spectrum of tensor perturbations in Finsler spacetime
Li, Xin
2015-01-01
We first investigate the gravitational wave in the flat Finsler spacetime. In the Finslerian universe, we derive the perturbed gravitational field equation with tensor perturbations. The Finslerian background spacetime breaks rotational symmetry and induces parity violation. Then we obtain the modified primordial power spectrum of tensor perturbations. The parity violation feature requires that the anisotropic effect contributes to $TT,TE,EE,BB$ angular correlation coefficients with $l'=l+1$ and $TB,EB$ with $l'=l$. The numerical results show that the anisotropic contributions to angular correlation coefficients depend on $m$, and $TE$ and $ET$ angular correlation coefficients are different.
Effects of motor programming on the power spectral density function of finger and wrist movements.
Van Galen, G P; Van Doorn, R R; Schomaker, L R
1990-11-01
Power spectral density analysis was applied to the frequency content of the acceleration signal of pen movements in line drawing. The relative power in frequency bands between 1 and 32 Hz was measured as a function of motoric and anatomic task demands. Results showed a decrease of power at the lower frequencies (1-4 Hz) of the spectrum and an increase in the middle (9-12 Hz), with increasing motor demands. These findings evidence the inhibition of visual control and the disinhibition of physiological tremor under conditions of increased programming demands. Adductive movements displayed less power than abductive movements in the lower end of the spectrum, with a simultaneous increase at the higher frequencies. The relevance of the method for the measurement of neuromotor noise as a possible origin of delays in motor behavior is discussed.
Time-variant power spectrum analysis for the detection of transient episodes in HRV signal.
Bianchi, A M; Mainardi, L; Petrucci, E; Signorini, M G; Mainardi, M; Cerutti, S
1993-02-01
A time-variant algorithm of autoregressive (AR) identification is introduced and applied to the heart rate variability (HRV) signal. The power spectrum is calculated from the AR coefficients derived from each single RR interval considered. Time-variant AR coefficients are determined through adaptive parametric identification with a forgetting factor which obtains weighed values on a running temporal window of 50 preceding measurements. Power spectrum density (PSD) is hence obtained at each cardiac cycle, making it possible to follow the dynamics of the spectral parameters on a beat-by-beat basis. These parameters are mainly the LF (low frequency) and the HF (high frequency) powers, and their ratio LF/HF. These together account for the balanced sympatho-vagal control mechanism affecting the heart rate. This method is applied to subjects suffering from transient ischemic attacks. The time variant spectral parameters suggest an early activation of LF component in the HRV power spectrum. It precedes by approximately 1.5-2 min the tachycardia and the ST displacement, generally indicative of the onset of an ischemic episode. The results suggest an arousal of sympathetic system before the acute attack.
Power spectrum for the Bose-Einstein condensate dark matter
Energy Technology Data Exchange (ETDEWEB)
Velten, Hermano, E-mail: velten@physik.uni-bielefeld.de [Departamento de Fisica, UFES, Vitoria, 29075-910 Espirito Santo (Brazil); Fakultaet fuer Physik, Universitaet Bielefeld, Postfach 100131, 33501 Bielefeld (Germany); Wamba, Etienne [Laboratory of Mechanics, Department of Physics, Faculty of Science, University of Yaounde I, P.O. Box 812, Yaounde (Cameroon)
2012-03-13
We assume that dark matter is composed of scalar particles that form a Bose-Einstein condensate (BEC) at some point during the cosmic evolution. Afterwards, cold dark matter is in the form of a condensate and behaves slightly different from the standard dark matter component. We study the large scale perturbative dynamics of the BEC dark matter in a model where this component coexists with baryonic matter and cosmological constant. The perturbative dynamics is studied using neo-Newtonian cosmology (where the pressure is dynamically relevant for the homogeneous and isotropic background) which is assumed to be correct for small values of the sound speed. We show that BEC dark matter effects can be seen in the matter power spectrum if the mass of the condensate particle lies in the range 15 MeV
Reconstructing the primordial power spectrum from the CMB
Energy Technology Data Exchange (ETDEWEB)
Gauthier, Christopher; Bucher, Martin, E-mail: cgauthie@apc.univ-paris7.fr, E-mail: bucher@apc.univ-paris7.fr [Laboratoire APC, Université Paris Diderot, Bâtiment Condorcet, 10 rue Alice Domon et Léonie Duquet, 75205 Paris Cedex 13 (France)
2012-10-01
We propose a straightforward and model independent methodology for characterizing the sensitivity of CMB and other experiments to wiggles, irregularities, and features in the primordial power spectrum. Assuming that the primordial cosmological perturbations are adiabatic, we present a function space generalization of the usual Fisher matrix formalism applied to a CMB experiment resembling Planck with and without ancillary data. This work is closely related to other work on recovering the inflationary potential and exploring specific models of non-minimal, or perhaps baroque, primordial power spectra. The approach adopted here, however, most directly expresses what the data is really telling us. We explore in detail the structure of the available information and quantify exactly what features can be reconstructed and at what statistical significance.
Reconstructing the primordial power spectrum from the CMB
Gauthier, Christopher
2012-01-01
We propose a straightforward and model independent methodology for characterizing the sensitivity of CMB and other experiments to wiggles, irregularities, and features in the primordial power spectrum. Assuming that the primordial cosmological perturbations are adiabatic, we present a function space generalization of the usual Fisher matrix formalism, applied to a CMB experiment resembling Planck with and without ancillary data. This work is closely related to other work on recovering the inflationary potential and exploring specific models of non-minimal, or perhaps baroque, primordial power spectra. The approach adopted here, however, most directly expresses what the data is really telling us. We explore in detail the structure of the available information and quantify exactly what features can be reconstructed and at what statistical significance.
Power spectrum for the Bose-Einstein condensate dark matter
Velten, Hermano
2011-01-01
We assume that dark matter is composed of scalar particles that form a Bose-Einstein condensate (BEC) at some point during the cosmic evolution. Afterwards, cold dark matter is in the form of a condensate and behaves slightly different from the standard dark matter component. We study the large scale perturbative dynamics of the BEC dark matter in a model where this component coexists with baryonic matter and cosmological constant. The perturbative dynamics is studied using neo- Newtonian cosmology (where the pressure is dynamically relevant for the homogeneous and isotropic background) which is assumed to be correct for small values of the sound speed. We show that BEC dark matter effects can be seen in the matter power spectrum if the mass of the condensate particle lies in the range 15meV < m < 700meV leading to a small, but perceptible, excess of power at large scales.
High-Power-Density Organic Radical Batteries.
Friebe, Christian; Schubert, Ulrich S
2017-02-01
Batteries that are based on organic radical compounds possess superior charging times and discharging power capability in comparison to established electrochemical energy-storage technologies. They do not rely on metals and, hence, feature a favorable environmental impact. They furthermore offer the possibility of roll-to-roll processing through the use of different printing techniques, which enables the cost-efficient fabrication of mechanically flexible devices. In this review, organic radical batteries are presented with the focus on the hitherto developed materials and the key properties thereof, e.g., voltage, capacity, and cycle life. Furthermore, basic information, such as significant characteristics, housing approaches, and applied additives, are presented and discussed in the context of organic radical batteries.
Cosmic Emulation: Fast Predictions for the Galaxy Power Spectrum
Kwan, Juliana; Habib, Salman; Padmanabhan, Nikhil; Finkel, Hal; Frontiere, Nick; Pope, Adrian
2013-01-01
The halo occupation distribution (HOD) approach has proven to be an effective method for modeling galaxy clustering and bias. In this approach, galaxies of a given type are probabilistically assigned to individual halos in N-body simulations. In this paper, we present a fast emulator for predicting the fully nonlinear galaxy power spectrum over a range of freely specifiable HOD modeling parameters. The emulator is constructed using results from 100 HOD models run on a large LCDM N-body simulation, with Gaussian Process interpolation applied to a PCA-based representation of the galaxy power spectrum. The total error is currently ~3% (~2% in the simulation and ~1% in the emulation process) from z=1 to z=0, over the considered parameter range. We use the emulator to investigate parametric dependencies in the HOD model, as well as the behavior of galaxy bias as a function of HOD parameters. The emulator is publicly available at http://www.hep.anl.gov/cosmology/CosmicEmu/emu.html.
First Results from COPSS: The CO Power Spectrum Survey
Keating, Garrett K; Marrone, Daniel P; DeBoer, David R; Heiles, Carl; Chang, Tzu-Ching; Carlstrom, John E; Greer, Christopher H; Hawkins, David; Lamb, James W; Leitch, Erik; Miller, Amber D; Muchovej, Stephen; Woody, David P
2015-01-01
We present constraints on the abundance of carbon-monoxide in the early Universe from the CO Power Spectrum Survey (COPSS). We utilize a data set collected between 2005 and 2008 using the Sunyaev-Zel'dovich Array (SZA), which were previously used to measure arcminute-scale fluctuations of the CMB. This data set features observations of 44 fields, covering an effective area of 1.7 square degrees, over a frequency range of 27 to 35 GHz. Using the technique of intensity mapping, we are able to probe the CO(1-0) transition, with sensitivity to spatial modes between $k=0.5{-}2\\ h\\,\\textrm{Mpc}^{-1}$ over a range in redshift of $z=2.3{-}3.3$, spanning a comoving volume of $3.6\\times10^{6}\\ h^{-3}\\,\\textrm{Mpc}^{3}$. We demonstrate our ability to mitigate foregrounds, and present estimates of the impact of continuum sources on our measurement. We constrain the CO power spectrum to $P_{\\textrm{CO}}<2.6\\times10^{4}\\ \\mu\\textrm{K}^{2} (h^{-1}\\,\\textrm{Mpc})^{3}$, or $\\Delta^{2}_{\\textrm{CO}}(k\\! = \\! 1 \\ h\\,\\textrm{...
Power Spectrum and Non-Gaussianities in Anisotropic Inflation
Dey, Anindya; Paban, Sonia
2014-01-01
We study the planar regime of curvature perturbations for single field inflationary models in an axially symmetric Bianchi I background. In a theory with standard scalar field action, the power spectrum for such modes has a pole as the planarity parameter goes to zero. We show that constraints from back reaction lead to a strong lower bound on the planarity parameter for high-momentum planar modes and use this bound to calculate the signal-to-noise ratio of the anisotropic power spectrum in the CMB, which in turn places an upper bound on the Hubble scale during inflation allowed in our model. We find that non-Gaussianities for these planar modes are enhanced for the flattened triangle and the squeezed triangle configurations, but show that the estimated values of the f_NL parameters remain well below the experimental bounds from the CMB for generic planar modes (other, more promising signatures are also discussed). For a standard action, f_NL from the squeezed configuration turns out to be larger compared to ...
Spectrum resolving power of hearing: measurements, baselines, and influence of maskers
Directory of Open Access Journals (Sweden)
Alexander Ya. Supin
2011-06-01
Full Text Available Contemporary methods of measurement of frequency tuning in the auditory system are reviewed. Most of them are based on the frequency-selective masking paradigm and require multi-point measurements (a number of masked thresholds should be measured to obtain a single frequency-tuning estimate. Therefore, they are rarely used for practical needs. As an alternative approach, frequency-selective properties of the auditory system may be investigated using probes with complex frequency spectrum patterns, in particular, rippled noise that is characterized by a spectrum with periodically alternating maxima and minima. The maximal ripple density discriminated by the auditory system is a convenient measure of the spectrum resolving power (SRP. To find the highest resolvable ripple density, a phase-reversal test has been suggested. Using this technique, normal SRP, its dependence on probe center frequency, spectrum contrast, and probe level were measured. The results were not entirely predictable by frequency-tuning data obtained by masking methods. SRP is influenced by maskers, with on- and off-frequency maskers influencing SRP very differently. Dichotic separation of the probe and masker results in almost complete release of SRP from influence of maskers.
Just enough inflation: power spectrum modifications at large scales
Cicoli, Michele; Dutta, Bhaskar; Pedro, Francisco G; Westphal, Alexander
2014-01-01
We show that models of `just enough' inflation, where the slow-roll evolution lasted only $50-60$ e-foldings, feature modifications of the CMB power spectrum at large angular scales. We perform a systematic and model-independent analysis of any possible non-slow-roll background evolution prior to the final stage of slow-roll inflation. We find a high degree of universality since most common backgrounds like fast-roll evolution, matter or radiation-dominance give rise to a power loss at large angular scales and a peak together with an oscillatory behaviour at scales around the value of the Hubble parameter at the beginning of slow-roll inflation. Depending on the value of the equation of state parameter, different pre-inflationary epochs lead instead to an enhancement of power at low-$\\ell$, and so seem disfavoured by recent observational hints for a lack of CMB power at $\\ell\\lesssim 40$. We also comment on the importance of initial conditions and the possibility to have multiple pre-inflationary stages.
Power-law modulation of the scalar power spectrum from a heavy field with a monomial potential
Huang, Qing-Guo
2016-01-01
The effects of heavy fields modulate the scalar power spectrum during inflation. We analytically calculate the modulations of the scalar power spectrum from a heavy field with a separable monomial potential, i.e. V(\\phi)~\\phi^n. In general the modulation is characterized by a power-law oscillation which is reduced to the logarithmic oscillation in the case of n=2.
Improving Free-Piston Stirling Engine Power Density
Briggs, Maxwell H.
2016-01-01
Analyses and experiments demonstrate the potential benefits of optimizing piston and displacer motion in a free piston Stirling Engine. Isothermal analysis shows the theoretical limits of power density improvement due to ideal motion in ideal Stirling engines. More realistic models based on nodal analysis show that ideal piston and displacer waveforms are not optimal, often producing less power than engines that use sinusoidal piston and displacer motion. Constrained optimization using nodal analysis predicts that Stirling engine power density can be increased by as much as 58% using optimized higher harmonic piston and displacer motion. An experiment is conducted in which an engine designed for sinusoidal motion is forced to operate with both second and third harmonics, resulting in a maximum piston power increase of 14%. Analytical predictions are compared to experimental data showing close agreement with indirect thermodynamic power calculations, but poor agreement with direct electrical power measurements.
Improving Power Density of Free-Piston Stirling Engines
Briggs, Maxwell H.; Prahl, Joseph M.; Loparo, Kenneth A.
2016-01-01
Analyses and experiments demonstrate the potential benefits of optimizing piston and displacer motion in a free-piston Stirling Engine. Isothermal analysis shows the theoretical limits of power density improvement due to ideal motion in ideal Stirling engines. More realistic models based on nodal analysis show that ideal piston and displacer waveforms are not optimal, often producing less power than engines that use sinusoidal piston and displacer motion. Constrained optimization using nodal analysis predicts that Stirling engine power density can be increased by as much as 58 percent using optimized higher harmonic piston and displacer motion. An experiment is conducted in which an engine designed for sinusoidal motion is forced to operate with both second and third harmonics, resulting in a piston power increase of as much as 14 percent. Analytical predictions are compared to experimental data and show close agreement with indirect thermodynamic power calculations, but poor agreement with direct electrical power measurements.
Statistical characteristics of observed Ly-$\\alpha$ forest and the shape of linear power spectrum
Demianski, M
2005-01-01
Properties of $\\sim$ 6 000 Ly-$\\alpha$ absorbers observed in 19 high resolution spectra of QSOs are investigated using the model of formation and evolution of DM structure elements based on the Zel'dovich theory. This model asserts that absorbers are formed in the course of both linear and nonlinear adiabatic or shock compression of dark matter (DM) and gaseous matter. It allows us to link the column density and overdensity of DM and gaseous components with the observed column density of neutral hydrogen, redshifts and Doppler parameters of absorbers and demonstrates that at high redshifts we observe a self similar period of structure evolution with the Gaussian initial perturbations. We show that the colder absorbers are associated with rapidly expanded regions of a galactic scale which represent large amplitude negative density perturbations. We extend and improve the method of measuring the power spectrum of initial perturbations proposed in Demia\\'nski & Doroshkevich (2003b). Our method links the obse...
The Atacama Cosmology Telescope: Two-Season ACTPol Lensing Power Spectrum
Sherwin, Blake D; Sehgal, Neelima; Madhavacheril, Mathew; Addison, Graeme E; Aiola, Simone; Allison, Rupert; Battaglia, Nicholas; Beall, James A; Becker, Daniel T; Bond, J Richard; Calabrese, Erminia; Datta, Rahul; Devlin, Mark J; Dunner, Rolando; Dunkley, Joanna; Fox, Anna E; Gallardo, Patricio; Halpern, Mark; Hasselfield, Matthew; Henderson, Shawn; Hill, J Colin; Hilton, Gene C; Hubmayr, Johannes; Hughes, John P; Hincks, Adam D; Hlozek, Renee; Huffenberger, Kevin M; Koopman, Brian; Kosowsky, Arthur; Louis, Thibaut; Maurin, Loic; McMahon, Jeff; Moodley, Kavilan; Naess, Sigurd; Nati, Federico; Newburgh, Laura; Niemack, Michael D; Page, Lyman A; Sievers, Jonathan; Spergel, David N; Staggs, Suzanne T; Thornton, Robert J; Van Lanen, Jeff; Vavagiakis, Eve; Wollack, Edward J
2016-01-01
We report a measurement of the power spectrum of cosmic microwave background (CMB) lensing from two seasons of Atacama Cosmology Telescope Polarimeter (ACTPol) CMB data. The CMB lensing power spectrum is extracted from both temperature and polarization data using quadratic estimators. We obtain results that are consistent with the expectation from the best-fit Planck LCDM model over a range of multipoles L=80-2100, with an amplitude of lensing A_lens = 1.06 +/- 0.15 (stat.) +/- 0.06 (sys.) relative to Planck. Our measurement of the CMB lensing power spectrum gives sigma_8 Omega_m^0.25 = 0.643 +/- 0.054; including baryon acoustic oscillation scale data, we constrain the amplitude of density fluctuations to be sigma_8 = 0.831 +/- 0.053. We also update constraints on the neutrino mass sum. We verify our lensing measurement with a number of null tests and systematic checks, finding no evidence of significant systematic errors. This measurement relies on a small fraction of the ACTPol data already taken; more prec...
Strong Lensing Probabilities in a Cosmological Model with a Running Primordial Power Spectrum
Zhang, T J; Yang, Z L; He, X T; Zhang, Tong-Jie; Chen, Da-Ming; Yang, Zhi-Liang; He, Xiang-Tao
2004-01-01
The combination of the first-year Wilkinson Microwave Anisotropy Probe (WMAP) data with other finer scale cosmic microwave background (CMB) experiments (CBI and ACBAR) and two structure formation measurements (2dFGRS and Lyman $\\alpha$ forest) suggest a $\\Lambda$CDM cosmological model with a running spectral power index of primordial density fluctuations. Motivated by this new result on the index of primordial power spectrum, we present the first study on the predicted lensing probabilities of image separation in a spatially flat $\\Lambda$CDM model with a running spectral index (RSI-$\\Lambda$CDM model). It is shown that the RSI-$\\Lambda$CDM model suppress the predicted lensing probabilities on small splitting angles of less than about 4$^{''}$ compared with that of standard power-law $\\Lambda$CDM (PL-$\\Lambda$CDM) model.
Increased Photovoltaic Power Output via Diffractive Spectrum Separation
Kim, Ganghun; Dominguez-Caballero, Jose A.; Lee, Howard; Friedman, Daniel J.; Menon, Rajesh
2013-03-01
In this Letter, we report the preliminary demonstration of a new paradigm for photovoltaic power generation that utilizes a broadband diffractive-optical element (BDOE) to efficiently separate sunlight into laterally spaced spectral bands. These bands are then absorbed by single-junction photovoltaic cells, whose band gaps correspond to the incident spectral bands. We designed such BDOEs by utilizing a modified version of the direct-binary-search algorithm. Gray scale lithography was used to fabricate these multilevel optics. They were experimentally characterized with an overall optical efficiency of 70% over a wavelength range of 350-1100 nm, which was in excellent agreement with simulation predictions. Finally, two prototype devices were assembled: one with a pair of copper indium gallium selenide based photovoltaic devices, and another with GaAs and c-Si photovoltaic devices. These devices demonstrated an increase in output peak electrical power of ˜42% and ˜22%, respectively, under white-light illumination. Because of the optical versatility and manufacturability of the proposed BDOEs, the reported spectrum-splitting approach provides a new approach toward low-cost solar power.
Increased photovoltaic power output via diffractive spectrum separation.
Kim, Ganghun; Dominguez-Caballero, Jose A; Lee, Howard; Friedman, Daniel J; Menon, Rajesh
2013-03-22
In this Letter, we report the preliminary demonstration of a new paradigm for photovoltaic power generation that utilizes a broadband diffractive-optical element (BDOE) to efficiently separate sunlight into laterally spaced spectral bands. These bands are then absorbed by single-junction photovoltaic cells, whose band gaps correspond to the incident spectral bands. We designed such BDOEs by utilizing a modified version of the direct-binary-search algorithm. Gray scale lithography was used to fabricate these multilevel optics. They were experimentally characterized with an overall optical efficiency of 70% over a wavelength range of 350-1100 nm, which was in excellent agreement with simulation predictions. Finally, two prototype devices were assembled: one with a pair of copper indium gallium selenide based photovoltaic devices, and another with GaAs and c-Si photovoltaic devices. These devices demonstrated an increase in output peak electrical power of ∼ 42% and ∼ 22%, respectively, under white-light illumination. Because of the optical versatility and manufacturability of the proposed BDOEs, the reported spectrum-splitting approach provides a new approach toward low-cost solar power.
Study of variations of radiofrequency power density from mobile phone base stations with distance.
Ayinmode, B O; Farai, I P
2013-10-01
The variations of radiofrequency (RF) radiation power density with distance around some mobile phone base stations (BTSs), in ten randomly selected locations in Ibadan, western Nigeria, were studied. Measurements were made with a calibrated hand-held spectrum analyser. The maximum Global System of Mobile (GSM) communication 1800 signal power density was 323.91 µW m(-2) at 250 m radius of a BTS and that of GSM 900 was 1119.00 µW m(-2) at 200 m radius of another BTS. The estimated total maximum power density was 2972.00 µW m(-2) at 50 m radius of a different BTS. This study shows that the maximum carrier signal power density and the total maximum power density from a BTS may be observed averagely at 200 and 50 m of its radius, respectively. The result of this study demonstrates that exposure of people to RF radiation from phone BTSs in Ibadan city is far less than the recommended limits by International scientific bodies.
High power density yeast catalyzed microbial fuel cells
Ganguli, Rahul
Microbial fuel cells leverage whole cell biocatalysis to convert the energy stored in energy-rich renewable biomolecules such as sugar, directly to electrical energy at high efficiencies. Advantages of the process include ambient temperature operation, operation in natural streams such as wastewater without the need to clean electrodes, minimal balance-of-plant requirements compared to conventional fuel cells, and environmentally friendly operation. These make the technology very attractive as portable power sources and waste-to-energy converters. The principal problem facing the technology is the low power densities compared to other conventional portable power sources such as batteries and traditional fuel cells. In this work we examined the yeast catalyzed microbial fuel cell and developed methods to increase the power density from such fuel cells. A combination of cyclic voltammetry and optical absorption measurements were used to establish significant adsorption of electron mediators by the microbes. Mediator adsorption was demonstrated to be an important limitation in achieving high power densities in yeast-catalyzed microbial fuel cells. Specifically, the power densities are low for the length of time mediator adsorption continues to occur. Once the mediator adsorption stops, the power densities increase. Rotating disk chronoamperometry was used to extract reaction rate information, and a simple kinetic expression was developed for the current observed in the anodic half-cell. Since the rate expression showed that the current was directly related to microbe concentration close to the electrode, methods to increase cell mass attached to the anode was investigated. Electrically biased electrodes were demonstrated to develop biofilm-like layers of the Baker's yeast with a high concentration of cells directly connected to the electrode. The increased cell mass did increase the power density 2 times compared to a non biofilm fuel cell, but the power density
Contribution of domain wall networks to the CMB power spectrum
Lazanu, A; Shellard, E P S
2015-01-01
We use three domain wall simulations from the radiation era to the late time dark energy domination era based on the PRS algorithm to calculate the energy-momentum tensor components of domain wall networks in an expanding universe. Unequal time correlators in the radiation, matter and cosmological constant epochs are calculated using the scaling regime of each of the simulations. The CMB power spectrum of a network of domain walls is determined. The first ever quantitative constraint for the domain wall surface tension is obtained using a Markov chain Monte Carlo method; an energy scale of domain walls of 0.93 MeV, which is close but below the Zel'dovich bound, is determined.
Contribution of domain wall networks to the CMB power spectrum
Directory of Open Access Journals (Sweden)
A. Lazanu
2015-07-01
Full Text Available We use three domain wall simulations from the radiation era to the late-time dark energy domination era based on the PRS algorithm to calculate the energy–momentum tensor components of domain wall networks in an expanding universe. Unequal time correlators in the radiation, matter and cosmological constant epochs are calculated using the scaling regime of each of the simulations. The CMB power spectrum of a network of domain walls is determined. The first ever quantitative constraint for the domain wall surface tension is obtained using a Markov chain Monte Carlo method; an energy scale of domain walls of 0.93 MeV, which is close but below the Zel'dovich bound, is determined.
Contribution of domain wall networks to the CMB power spectrum
Energy Technology Data Exchange (ETDEWEB)
Lazanu, A., E-mail: A.Lazanu@damtp.cam.ac.uk [Centre for Theoretical Cosmology, Department of Applied Mathematics and Theoretical Physics, Wilberforce Road, Cambridge CB3 0WA (United Kingdom); Martins, C.J.A.P., E-mail: Carlos.Martins@astro.up.pt [Centro de Astrofísica, Universidade do Porto, Rua das Estrelas, 4150-762 Porto (Portugal); Instituto de Astrofísica e Ciências do Espaço, CAUP, Rua das Estrelas, 4150-762 Porto (Portugal); Shellard, E.P.S., E-mail: E.P.S.Shellard@damtp.cam.ac.uk [Centre for Theoretical Cosmology, Department of Applied Mathematics and Theoretical Physics, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)
2015-07-30
We use three domain wall simulations from the radiation era to the late-time dark energy domination era based on the PRS algorithm to calculate the energy–momentum tensor components of domain wall networks in an expanding universe. Unequal time correlators in the radiation, matter and cosmological constant epochs are calculated using the scaling regime of each of the simulations. The CMB power spectrum of a network of domain walls is determined. The first ever quantitative constraint for the domain wall surface tension is obtained using a Markov chain Monte Carlo method; an energy scale of domain walls of 0.93 MeV, which is close but below the Zel'dovich bound, is determined.
Design of High Power Density Amplifiers: Application to Ka Band
Passi, Davide; Leggieri, Alberto; Di Paolo, Franco; Bartocci, Marco; Tafuto, Antonio
2017-06-01
Recent developments in the design of high-power-high-frequency amplifiers are assessed in this paper by the analysis and measurements of a high power density amplifier operating in the Ka Band. Design procedure is presented and a technical investigation is reported. The proposed device has shown over 23% of useful frequency bandwidth. It is an ensemble of 16 monolithic solid state power amplifiers that employees mixed technologies as spatial and planar combiners. Test performed have given maximum delivered power of 47.2 dBm.
Contribution of Cross-Correlations to the 21cm Angular Power Spectrum in the Epoch of Reionization
Zheng, Qian
2009-01-01
Measurement of the 21cm hyperfine transition of neutral hydrogen provides a unique probe of the epoch of reionization and the Dark Ages. Three major mechanisms are believed to dominate the radiation process: emission from neutral hydrogen surrounding the ionized bubbles of first galaxies and/or quasars, emission from neutral hydrogen inside minihalos, and absorption of diffuse neutral hydrogen against the cosmic microwave background. In the present work, by simply combining the existing analytic models for the three mechanisms, we investigate the contribution of cross-correlation between these three components to the total 21cm angular power spectrum, in the sense that neutral hydrogen associated with different radiation processes traces the large-scale structures of underlying density perturbations. While the overall 21cm power spectrum remains almost unchanged with the inclusion of the cross-correlations, the cross-correlation may play a key role in the determination of the 21cm power spectrum during the tr...
Thermodynamic analysis of Thermophotovoltaic Efficiency and Power Density Tradeoffs
Energy Technology Data Exchange (ETDEWEB)
P.F. Baldasara; J.E. Reynolds; G.W. Charache; D.M. DePoy; C.T. Ballinger; T. Donovan; J.M. Borrego
2000-02-22
This report presents an assessment of the efficiency and power density limitations of thermophotovoltaic (TPV) energy conversion systems for both ideal (radiative-limited) and practical (defect-limited) systems. Thermodynamics is integrated into the unique process physics of TPV conversion, and used to define the intrinsic tradeoff between power density and efficiency. The results of the analysis reveal that the selection of diode bandgap sets a limit on achievable efficiency well below the traditional Carnot level. In addition it is shown that filter performance dominates diode performance in any practical TPV system and determines the optimum bandgap for a given radiator temperature. It is demonstrated that for a given radiator temperature, lower bandgap diodes enable both higher efficiency and power density when spectral control limitations are included. The goal of this work is to provide a better understanding of the basic system limitations that will enable successful long-term development of TPV energy conversion technology.
Roundoff noise analysis for digital signal power processors using Welch's power spectrum estimation
Chi, Chong-Yung; Long, David; Li, Fuk-Kwok
1987-01-01
The noise due to finite-word-length effects is analyzed for digital-signal power processors using Welch's power-spectrum estimation technique to measure the power of Gaussian random signals over a frequency band of interest. The input of the digital signal processor contains a finite-length time interval in which the true Gaussian signal is contaminated by Gaussian noise. The roundoff noise-to-signal ratio in the measurement of the signal power is derived, and computer simulations which validate the analytical results are presented. These results can be used in tradeoff studies of hardware design, such as the number of bits required at each processing stage. The results presented in this paper are currently being used in the design of a digital Doppler processor (Chi et al., 1986) for a radar scatterometer.
Demiański, M
2015-01-01
To restore the evolutionary history of the Dark Matter (DM) dominated objects -- galaxies and clusters of galaxies. Analyze the observational data to reveal correlations between the virial mass, $M_{vir}$, of halos and main properties of their central cores, namely, the mean DM density, pressure and entropy, and the redshifts of halo formation, $z_f$. These correlations indicate a high degree of self similarity of both the process of halos formation and the internal structure of relaxed halos. We confirm the CDM--like shape of the small scale power spectrum. However our reconstruction of evolutionary history of observed objects differs from expectations of the standard $\\Lambda$CDM cosmology and requires either multicomponent composition of DM or more complex primordial power spectrum of density perturbations with significant excess of power at scales of clusters of galaxies and larger. This approach seems to be quite efficient and suitably supplements the current investigations of galaxies at large redshifts...
BP-Neural-Network-Based Tool Wear Monitoring by Using Wavelet Decomposition of the Power Spectrum
Institute of Scientific and Technical Information of China (English)
ZHENG Jian-ming; XI Chang-qing; LI Yan; XIAO Ji-ming
2004-01-01
In a drilling process, the power spectrum of the drilling force is related to the tool wear and is widely applied in the monitoring of tool wear. But the feature extraction and identification of the power spectrum have always been an unresolved difficult problem. This paper solves it through decomposition of the power spectrum in multilayers using wavelet transform and extraction of the low frequency decomposition coefficient us the envelope information of the power spectrum. Intelligent identification of the tool wear status is achieved in the drilling process through fusing the wavelet decomposition coefficient of the power spectrum by using a BP ( Back Propagation) neural network. The experimental results show that the features of the power spectrum can be extracted efficiently through this method, and the trained neural networks show high identification precision and the ability of extension.
The use of the power density for identifying reconnection regions
Hamrin, M.; Andersson, L.; Vaivads, A.; Pitkänen, T.; Gunell, H.
2015-10-01
In the vicinity of magnetic reconnection, magnetic energy is transferred into kinetic energy. A reconnection region hence corresponds to a load, and it should manifest itself as large and positive values of the power density, E·J ≫ 0, where E is the electric field and J the current density. In this article we analyze Cluster plasma sheet data from 2001-2004 to investigate the use of the power density for identifying possible magnetic reconnection events from large sets of observed data. From theoretical arguments we show that an event with E·J≳20 pW/m3 in the Earth's magnetotail observed by the Cluster instruments (X potential reconnection regions, but selected events must be reviewed separately to confirm any possible reconnection signatures by looking for other signatures such as Hall electric and magnetic fields and reconnection jets. The power density can be computed from multispacecraft data, and we argue that the power density can be used as a tool for identifying possible reconnection events from large sets of data, e.g., from the Cluster and the Magnetospheric Multiscale missions.
Discussion of the specific method of power spectral density
Ren Huan; Jiang Xiao Dong; Peng Jing; Ye Lin; Huang Zu Xin; Tang Can
2002-01-01
The wavefront power spectral density (PSD) can give the spatial frequency distribution of wavefront aberration, limit the waviness and the roughness, and specify the large components employed in high power density solid-state laser for inertial confinement fusion (ICF). The definition and the calculation of the PSD are given. In experiment, a large phase shifting Fizeau interferometer was used to test the transmissive wavefront of a Nd glass, creating the one dimension wavefront PSD. Same time, relationship between the PSD and the RMS is shown
Cooling Concepts for High Power Density Magnetic Devices
Biela, Juergen; Kolar, Johann W.
In the area or power electronics there is a general trend to higher power densities. In order to increase the power density the systems must be designed optimally concerning topology, semiconductor selection, etc. and the volume of the components must be decreased. The decreasing volume comes along with a reduced surface for cooling. Consequently, new cooling methods are required. In the paper an indirect air cooling system for magnetic devices which combines the transformer with a heat sink and a heat transfer component is presented. Moreover, an analytic approach for calculating the temperature distribution is derived and validated by measurements. Based on these equations a transformer with an indirect air cooling system is designed for a 10kW telecom power supply.
Li, Fangda; Law, Nicholas M
2012-01-01
The dark matter enclosed in a density perturbation with a large initial amplitude (delta-rho/rho > 1e-3) collapses shortly after recombination and forms an ultracompact minihalo (UCMH). Their high central densities make UCMHs especially suitable for detection via astrometric microlensing: as the UCMH moves, it changes the apparent position of background stars. A UCMH with a mass larger than a few solar masses can produce a distinctive astrometric microlensing signal that is detectable by the space astrometry mission Gaia. If Gaia does not detect gravitational lensing by any UCMHs, then it establishes an upper limit on their abundance and constrains the amplitude of the primordial power spectrum for k~3500 Mpc^{-1}. These constraints complement the upper bound on the amplitude of the primordial power spectrum derived from limits on gamma-ray emission from UCMHs because the astrometric microlensing signal produced by an UCMH is maximized if the dark-matter annihilation rate is too low to affect the UCMH's densi...
Fisher, K B
1993-01-01
We examine the nature of galaxy clustering in redshift space using a method based on an expansion of the galaxian density field in Spherical Harmonics and linear theory. We derive a compact and self-consistent expression for the distortion when applied to flux limited redshift surveys. The amplitude of the distortion is controlled by the combination of the density and bias parameters, $\\beta\\equiv\\Omega_\\circ^{0.6}/b$ as well as the shape of the real space power spectrum, $P(k)$ (characterized by a shape parameter $\\Gamma$), and its normalization, $\\sigma_8$; we exploit this fact to derive a maximum likelihood estimator for $\\beta$, $\\Gamma$, and $\\sigma_8$. We check our formalism using $N$-body simulations and demonstrate it provides an unbiased estimate of $\\beta$ when the amplitude and shape of the galaxy power spectrum is known. Application of the technique to the 1.2 Jy \\iras\\ redshift survey yields $\\beta =0.94\\pm 0.17$ and $\\Gamma=0.17\\pm0.05$ (1-$\\sigma$) when $\\sigma_8$ is held fixed at its best valu...
Borde, Arnaud; Palanque-Delabrouille, Nathalie; Rossi, Graziano; Viel, Matteo; Bolton, James S.; Yèche, Christophe; LeGoff, Jean-Marc; Rich, Jim
2014-07-01
Current experiments are providing measurements of the flux power spectrum from the Lyman-α forests observed in quasar spectra with unprecedented accuracy. Their interpretation in terms of cosmological constraints requires specific simulations of at least equivalent precision. In this paper, we present a suite of cosmological N-body simulations with cold dark matter and baryons, specifically aiming at modeling the low-density regions of the inter-galactic medium as probed by the Lyman-α forests at high redshift. The simulations were run using the GADGET-3 code and were designed to match the requirements imposed by the quality of the current SDSS-III/BOSS or forthcoming SDSS-IV/eBOSS data. They are made using either 2 × 7683 simeq 1 billion or 2 × 1923 simeq 14 million particles, spanning volumes ranging from (25 Mpc h-1)3 for high-resolution simulations to (100 Mpc h-1)3 for large-volume ones. Using a splicing technique, the resolution is further enhanced to reach the equivalent of simulations with 2 × 30723 simeq 58 billion particles in a (100 Mpc h-1)3 box size, i.e. a mean mass per gas particle of 1.2 × 105Msolar h-1. We show that the resulting power spectrum is accurate at the 2% level over the full range from a few Mpc to several tens of Mpc. We explore the effect on the one-dimensional transmitted-flux power spectrum of four cosmological parameters (ns, σ8, Ωm and H0) and two astrophysical parameters (T0 and γ) that are related to the heating rate of the intergalactic medium. By varying the input parameters around a central model chosen to be in agreement with the latest Planck results, we built a grid of simulations that allows the study of the impact on the flux power spectrum of these six relevant parameters. We improve upon previous studies by not only measuring the effect of each parameter individually, but also probing the impact of the simultaneous variation of each pair of parameters. We thus provide a full second-order expansion, including
Inverse Calculation of Power Density for Laser Surface Treatment
Römer, G.R.B.E.; Meijer, J.
2000-01-01
Laser beam surface treatment requires a well-defined temperature profile. In this paper an analytic method is presented to solve the inverse problem of heat conduction in solids, based on the 2-dimensional Fourier transform. As a result, the required power density profile of the laser beam can be ca
Inverse calculation of power density for laser surface treatment
Römer, Gerardus Richardus, Bernardus, Engelina; Meijer, J.
2000-01-01
Laser beam surface treatment requires a well-defined temperature profile. In this paper an analytic method is presented to solve the inverse problem of heat conduction in solids, based on the 2-dimensional Fourier transform. As a result, the required power density profile of the laser beam can be
Inverse calculation of power density for laser surface treatment
Römer, Gerardus Richardus, Bernardus, Engelina; Meijer, J.
2000-01-01
Laser beam surface treatment requires a well-defined temperature profile. In this paper an analytic method is presented to solve the inverse problem of heat conduction in solids, based on the 2-dimensional Fourier transform. As a result, the required power density profile of the laser beam can be ca
Aghanim, N; Ashdown, M; Aumont, J; Ballardini, M; Banday, A J; Barreiro, R B; Bartolo, N; Basak, S; Benabed, K; Bersanelli, M; Bielewicz, P; Bonaldi, A; Bonavera, L; Bond, J R; Borrill, J; Bouchet, F R; Burigana, C; Calabrese, E; Cardoso, J -F; Challinor, A; Chiang, H C; Colombo, L P L; Combet, C; Crill, B P; Curto, A; Cuttaia, F; de Bernardis, P; de Rosa, A; de Zotti, G; Delabrouille, J; Di Valentino, E; Dickinson, C; Diego, J M; Doré, O; Ducout, A; Dupac, X; Dusini, S; Efstathiou, G; Elsner, F; Enßlin, T A; Eriksen, H K; Fantaye, Y; Finelli, F; Forastieri, F; Frailis, M; Franceschi, E; Frolov, A; Galeotta, S; Galli, S; Ganga, K; Génova-Santos, R T; Gerbino, M; González-Nuevo, J; Górski, K M; Gruppuso, A; Gudmundsson, J E; Herranz, D; Hivon, E; Huang, Z; Jaffe, A H; Jones, W C; Keihänen, E; Keskitalo, R; Kiiveri, K; Kim, J; Kisner, T S; Knox, L; Krachmalnicoff, N; Kunz, M; Kurki-Suonio, H; Lagache, G; Lamarre, J -M; Lasenby, A; Lattanzi, M; Lawrence, C R; Jeune, M Le; Levrier, F; Lewis, A; Lilje, P B; Lilley, M; Lindholm, V; López-Caniego, M; Lubin, P M; Ma, Y -Z; Macías-Pérez, J F; Maggio, G; Maino, D; Mandolesi, N; Mangilli, A; Maris, M; Martin, P G; Martínez-González, E; Matarrese, S; Mauri, N; McEwen, J D; Meinhold, P R; Mennella, A; Migliaccio, M; Millea, M; Miville-Deschênes, M -A; Molinari, D; Moneti, A; Montier, L; Morgante, G; Moss, A; Narimani, A; Natoli, P; Oxborrow, C A; Pagano, L; Paoletti, D; Patanchon, G; Patrizii, L; Pettorino, V; Piacentini, F; Polastri, L; Polenta, G; Puget, J -L; Rachen, J P; Racine, B; Reinecke, M; Remazeilles, M; Renzi, A; Rossetti, M; Roudier, G; Rubiño-Martín, J A; Ruiz-Granados, B; Salvati, L; Sandri, M; Savelainen, M; Scott, D; Sirignano, C; Sirri, G; Stanco, L; Suur-Uski, A -S; Tauber, J A; Tavagnacco, D; Tenti, M; Toffolatti, L; Tomasi, M; Tristram, M; Trombetti, T; Valiviita, J; Van Tent, F; Vielva, P; Villa, F; Vittorio, N; Wandelt, B D; Wehus, I K; White, M; Zacchei, A; Zonca, A
2016-01-01
The six parameters of the standard $\\Lambda$CDM model have best-fit values derived from the Planck temperature power spectrum that are shifted somewhat from the best-fit values derived from WMAP data. These shifts are driven by features in the Planck temperature power spectrum at angular scales that had never before been measured to cosmic-variance level precision. We investigate these shifts to determine whether they are within the range of expectation and to understand their origin in the data. Taking our parameter set to be the optical depth of the reionized intergalactic medium $\\tau$, the baryon density $\\omega_{\\rm b}$, the matter density $\\omega_{\\rm m}$, the angular size of the sound horizon $\\theta_*$, the spectral index of the primordial power spectrum, $n_{\\rm s}$, and $A_{\\rm s}e^{-2\\tau}$ (where $A_{\\rm s}$ is the amplitude of the primordial power spectrum), we examine the change in best-fit values between a WMAP-like large angular-scale data set (with multipole moment $\\ell800$, or splitting at ...
Nasir, Fahad; Becker, George D
2016-01-01
We use cosmological hydrodynamical simulations to assess the feasibility of constraining the thermal history of the intergalactic medium during reionisation with the Ly$\\alpha$ forest at $z \\simeq 5$. Pressure smoothing has a measurable impact on the transmitted flux power spectrum that can be isolated from Doppler broadening at this redshift. We parameterise the effect of pressure smoothing on the power spectrum using the cumulative energy per proton, $u_0$, deposited into a gas parcel at the mean background density, a quantity that is tightly linked with the integrated thermal history and the gas density power spectrum in the simulations. We construct mock observations of the line of sight Ly$\\alpha$ forest power spectrum and use a Markov Chain Monte Carlo approach to recover $u_{0}$ at redshifts $5 \\leq z \\leq 12$. A statistical uncertainty of $\\sim 20$ per cent is expected (at 68 per cent confidence) at $z\\simeq 5$ using high resolution spectra with a total redshift path length of $\\Delta z=4$ and a typic...
Noise power spectrum measurements under nonuniform gains and their compensations
Kim, Dong Sik; Kim, Eun; Shin, Choul Woo
2016-03-01
The fixed pattern noise, which is due to the nonuniform amplifier gains and scintillator sensitivities, should be alleviated in radiography imaging and should have less influence on measuring the noise power spectrum (NPS) of the radiography detector. In order to reduce the influence, background trend removing methods, which are based on low-pass filtering, polynomial fitting, and subtracting the average image of the uniform exposure images, are traditionally employed in the literature. In terms of removing the fixed pattern noise, the subtraction method shows a good performance. However, the number of images to be averaged is practically finite and thus the noise contained in the average image contaminates the image difference and inflates the NPS curve. In this paper, an image formation model considering the nonuniform gain is constructed and two measuring methods, which are based on the subtraction and gain correction, respectively, are considered. In order to accurately measure a normalized NPS (NNPS) in the measuring methods, the number of images to be averaged is considered for NNPS compensations. For several flat-panel radiography detectors, the NNPS measurements are conducted and compared with conventional approaches, which have no compensation stages. Through experiments it is shown that the compensation can provide accurate NNPS measurements less influenced by the fixed pattern noise.
Perturbative approach to covariance matrix of the matter power spectrum
Mohammed, Irshad; Vlah, Zvonimir
2016-01-01
We evaluate the covariance matrix of the matter power spectrum using perturbation theory up to dominant terms at 1-loop order and compare it to numerical simulations. We decompose the covariance matrix into the disconnected (Gaussian) part, trispectrum from the modes outside the survey (beat coupling or super-sample variance), and trispectrum from the modes inside the survey, and show how the different components contribute to the overall covariance matrix. We find the agreement with the simulations is at a 10\\% level up to $k \\sim 1 h {\\rm Mpc^{-1}}$. We show that all the connected components are dominated by the large-scale modes ($k<0.1 h {\\rm Mpc^{-1}}$), regardless of the value of the wavevectors $k,\\, k'$ of the covariance matrix, suggesting that one must be careful in applying the jackknife or bootstrap methods to the covariance matrix. We perform an eigenmode decomposition of the connected part of the covariance matrix, showing that at higher $k$ it is dominated by a single eigenmode. The full cova...
Perturbative approach to covariance matrix of the matter power spectrum
Energy Technology Data Exchange (ETDEWEB)
Mohammed, Irshad [Fermilab; Seljak, Uros [UC, Berkeley, Astron. Dept.; Vlah, Zvonimir [Stanford U., ITP
2016-06-30
We evaluate the covariance matrix of the matter power spectrum using perturbation theory up to dominant terms at 1-loop order and compare it to numerical simulations. We decompose the covariance matrix into the disconnected (Gaussian) part, trispectrum from the modes outside the survey (beat coupling or super-sample variance), and trispectrum from the modes inside the survey, and show how the different components contribute to the overall covariance matrix. We find the agreement with the simulations is at a 10\\% level up to $k \\sim 1 h {\\rm Mpc^{-1}}$. We show that all the connected components are dominated by the large-scale modes ($k<0.1 h {\\rm Mpc^{-1}}$), regardless of the value of the wavevectors $k,\\, k'$ of the covariance matrix, suggesting that one must be careful in applying the jackknife or bootstrap methods to the covariance matrix. We perform an eigenmode decomposition of the connected part of the covariance matrix, showing that at higher $k$ it is dominated by a single eigenmode. The full covariance matrix can be approximated as the disconnected part only, with the connected part being treated as an external nuisance parameter with a known scale dependence, and a known prior on its variance for a given survey volume. Finally, we provide a prescription for how to evaluate the covariance matrix from small box simulations without the need to simulate large volumes.
High Resolution Observations of the CMB Power Spectrum with ACBAR
Kuo, C L; Bock, J J; Cantalupo, C M; Daub, M D; Goldstein, J; Holzapfel, W L; Lange, A E; Lueker, M; Newcomb, M; Peterson, J B; Ruhl, J; Runyan, M C; Torbet, E
2004-01-01
We report the first measurements of anisotropy in the cosmic microwave background (CMB) radiation with the Arcminute Cosmology Bolometer Array Receiver (ACBAR). The instrument was installed on the 2.1m Viper telescope at the South Pole in January 2001; the data presented here are the product of observations up to and including July 2002. The two deep fields presented here, have had offsets removed by subtracting lead and trail observations and cover approximately 24 deg^2 of sky selected for low dust contrast. These results represent the highest signal to noise observations of CMB anisotropy to date; in the deepest 150GHz band map, we reached an RMS of 8.0\\mu K per 5' beam. The 3 degree extent of the maps, and small beamsize of the experiment allow the measurement of the CMB anisotropy power spectrum over the range \\ell = 150-3000 with resolution of \\Delta \\ell=150. The contributions of galactic dust and radio sources to the observed anisotropy are negligible and are removed in the analysis. The resulting pow...
Modulation of EMG power spectrum frequency during motor imagery.
Lebon, F; Rouffet, D; Collet, C; Guillot, A
2008-04-25
To provide evidence that motor imagery (MI) is accompanied by improvement of intramuscular conduction velocity (CV), we investigated surface electromyographic (EMG) activity of 3 muscles during the elbow flexion/extension. Thirty right-handed participants were asked to lift or to imagine lifting a weighted dumbbell under 3 types of muscular contractions, i.e. concentric, isometric and eccentric, taken as independent variables. The EMG activity of the agonist (long and short heads of biceps brachii) and the antagonist (long portion of triceps brachii) muscles was recorded and processed to determine the median frequency (MF) of EMG power spectrum as dependant variable. The MF was significantly higher during the MI sessions than during the resting condition while the participants remained strictly motionless. Moreover, the MF during imagined concentric contraction was significantly higher than during the eccentric. Thus, the MF variation was correlated to the type of contraction the muscle produced. During MI, the EMG patterns corresponding to each type of muscle contraction remained comparable to those observed during actual movement. In conclusion, specific motor programming is hypothesized to be performed as a function of muscle contraction type during MI.
Perturbative approach to covariance matrix of the matter power spectrum
Mohammed, Irshad; Seljak, Uroš; Vlah, Zvonimir
2017-04-01
We evaluate the covariance matrix of the matter power spectrum using perturbation theory up to dominant terms at 1-loop order and compare it to numerical simulations. We decompose the covariance matrix into the disconnected (Gaussian) part, trispectrum from the modes outside the survey (supersample variance) and trispectrum from the modes inside the survey, and show how the different components contribute to the overall covariance matrix. We find the agreement with the simulations is at a 10 per cent level up to k ˜ 1 h Mpc-1. We show that all the connected components are dominated by the large-scale modes (k covariance matrix, suggesting that one must be careful in applying the jackknife or bootstrap methods to the covariance matrix. We perform an eigenmode decomposition of the connected part of the covariance matrix, showing that at higher k, it is dominated by a single eigenmode. The full covariance matrix can be approximated as the disconnected part only, with the connected part being treated as an external nuisance parameter with a known scale dependence, and a known prior on its variance for a given survey volume. Finally, we provide a prescription for how to evaluate the covariance matrix from small box simulations without the need to simulate large volumes.
Estimating the power spectrum covariance matrix with fewer mock samples
Pearson, David W
2015-01-01
The covariance matrices of power-spectrum (P(k)) measurements from galaxy surveys are difficult to compute theoretically. The current best practice is to estimate covariance matrices by computing a sample covariance of a large number of mock catalogues. The next generation of galaxy surveys will require thousands of large volume mocks to determine the covariance matrices to desired accuracy. The errors in the inverse covariance matrix are larger and scale with the number of P(k) bins, making the problem even more acute. We develop a method of estimating covariance matrices using a theoretically justified, few-parameter model, calibrated with mock catalogues. Using a set of 600 BOSS DR11 mock catalogues, we show that a seven parameter model is sufficient to fit the covariance matrix of BOSS DR11 P(k) measurements. The covariance computed with this method is better than the sample covariance at any number of mocks and only ~100 mocks are required for it to fully converge and the inverse covariance matrix conver...
Directory of Open Access Journals (Sweden)
Abhijit Sinha
2014-01-01
Full Text Available A comparative analysis on thermodynamic efficiency based on maximum power & power density conditions have been performed for a solar-driven Carnot heat engine with internal irreversibility. In this analysis, the heat transfer from the hot reservoir is to be in the radiation mode and the heat transfer to the cold reservoir is to be in the convection mode. The thermodynamic efficiency function, power & power density functions have been derived and maximization of the power functions have been performed for various design parameters. From the optimum conditions, the thermal efficiencies at maximum power and power densities have been obtained. The effects of internal irreversibility, extreme temperature ratios & specific engine size in area ratio between the hot & cold reservoirs as various design parameters on thermodynamic efficiencies have been investigated for both the conditions. The efficiencies have been compared with Curzon-Ahlborn & Carnot efficiencies respectively.The analysis showed that the efficiency at maximum power output is greater than the efficiency at maximum power density. And the efficiencies can be greater than the Curzon- Ahlborn`s efficiency only for low values of design parameters.
Yip, Ngai Yin; Vermaas, David A; Nijmeijer, Kitty; Elimelech, Menachem
2014-05-06
Reverse electrodialysis (RED) can harness the Gibbs free energy of mixing when fresh river water flows into the sea for sustainable power generation. In this study, we carry out a thermodynamic and energy efficiency analysis of RED power generation, and assess the membrane power density. First, we present a reversible thermodynamic model for RED and verify that the theoretical maximum extractable work in a reversible RED process is identical to the Gibbs free energy of mixing. Work extraction in an irreversible process with maximized power density using a constant-resistance load is then examined to assess the energy conversion efficiency and power density. With equal volumes of seawater and river water, energy conversion efficiency of ∼ 33-44% can be obtained in RED, while the rest is lost through dissipation in the internal resistance of the ion-exchange membrane stack. We show that imperfections in the selectivity of typical ion exchange membranes (namely, co-ion transport, osmosis, and electro-osmosis) can detrimentally lower efficiency by up to 26%, with co-ion leakage being the dominant effect. Further inspection of the power density profile during RED revealed inherent ineffectiveness toward the end of the process. By judicious early discontinuation of the controlled mixing process, the overall power density performance can be considerably enhanced by up to 7-fold, without significant compromise to the energy efficiency. Additionally, membrane resistance was found to be an important factor in determining the power densities attainable. Lastly, the performance of an RED stack was examined for different membrane conductivities and intermembrane distances simulating high performance membranes and stack design. By thoughtful selection of the operating parameters, an efficiency of ∼ 37% and an overall gross power density of 3.5 W/m(2) represent the maximum performance that can potentially be achieved in a seawater-river water RED system with low
Red, Straight, no bends: primordial power spectrum reconstruction from CMB and large-scale structure
Ravenni, Andrea; Cuesta, Antonio J
2016-01-01
We present a minimally parametric, model independent reconstruction of the shape of the primordial power spectrum. Our smoothing spline technique is well-suited to search for smooth features such as deviations from scale invariance, and deviations from a power law such as running of the spectral index or small-scale power suppression. We use a comprehensive set of the state-of the art cosmological data: {\\it Planck} observations of the temperature and polarisation anisotropies of the cosmic microwave background, WiggleZ and Sloan Digital Sky Survey Data Release 7 galaxy power spectra and the Canada-France-Hawaii Lensing Survey correlation function. This reconstruction strongly supports the evidence for a power law primordial power spectrum with a red tilt and disfavours deviations from a power law power spectrum including small-scale power suppression such as that induced by significantly massive neutrinos. This offers a powerful confirmation of the inflationary paradigm, justifying the adoption of the inflat...
The Atacama Cosmology Telescope: A Measurement of the Primordial Power Spectrum
Hlozek, Renee; Dunkley, Joanna; Addison, Graeme; Appel, John William; Bond, J. Richard; Carvalho, C. Sofia; Das, Sudeep; Devlin, Mark J.; Duenner, Rolando; Essinger-Hileman, Thomas;
2011-01-01
We present constraints on the primordial power spectrum of adiabatic fluctuations using data from the 2008 Southern Survey of the Atacama Cosmology Telescope (ACT). The angular resolution of ACT provides sensitivity to scales beyond l = 1000 for resolution of multiple peaks in the primordial temperature power spectrum, which enables us to probe the primordial power spectrum of adiabatic scalar perturbations with wavenumbers up to k approx. = 0.2 Mp/c. We find no evidence for deviation from power-law fluctuations over two decades in scale. Matter fluctuations inferred from the primordial temperature power spectrum evolve over cosmic time and can be used to predict the matter power spectrum at late times; we illustrate the overlap of the matter power inferred from CMB measurements (which probe the power spectrum in thc linear regime) with existing probes of galaxy clustering, cluster abundances and weak lensing constraints on the primordial power. This highlights the range of scales probed by current measurement.s of the matter power spectrum.
Nanostructured thin solid oxide fuel cells with high power density.
Ignatiev, Alex; Chen, Xin; Wu, Naijuan; Lu, Zigui; Smith, Laverne
2008-10-28
Nanostructured thin film solid oxide fuel cells (SOFC) have been developed for reduced temperature operation, with high power density, and to be self reforming. A thin film electrolyte (1-2 microm thickness), e.g., yttria-stabilized zirconia (YSZ), is deposited on a nickel foil substrate. The electrolyte thin film is polycrystalline when deposited on a polycrystalline nickel foil substrate, and is (100) textured when deposited on an atomically textured nickel foil substrate. The Ni foil substrate is then converted into a porous SOFC anode by photolithographic patterning and etching to develop porosity. A composite La(0.5)Sr(0.5)CoO(3) cathode is then deposited on the thin film electrolyte. The resultant thin film hetero structure fuel cells have operated at a significantly reduced temperature: as low as 470 degrees C, with a maximum power density of 140 mW cm(-2) at 575 degrees C, and an efficiency of >50%. This drastic reduction in operating temperature for an SOFC now also allows for the use of hydrocarbon fuels without the need for a separate reformer as the nickel anode effectively dissociates hydrocarbons within this temperature range. These nanostructured fuel cells show excellent potential for high power density, small volume, high efficiency fuel cells for power generation applications.
Corrections to the density-functional theory electronic spectrum: Copper phthalocyanine
DEFF Research Database (Denmark)
Vazquez, Hector; Jelinek, P.; Brandbyge, Mads;
2009-01-01
A method for improving the electronic spectrum of standard Density-Functional Theory (DFT) calculations (i.e., LDA or GGA approximations) is presented, and its application is discussed for the case of the copper phthalocyanine (CuPc) molecule. The method is based on a treatment of exchange and co...
Interaction of high-power laser radiation with low-density polymer aerogels
Kaur, Ch; Chaurasia, Sh; Borisenko, N. G.; Orekhov, A. S.; Leshma, P.; Pimenov, V. G.; Sklizkov, G. V.; Akunets, A. A.; Deo, M. N.
2017-06-01
The interaction of high-power subnanosecond laser pulses with low-density targets of cellulose triacetate polymer is considered. An Nd-glass laser setup provides a focal spot intensity of over 1014 W cm-2. An investigation is made of absorption of laser radiation, laser-to-X-ray energy conversion, spectra of ions emitted from the plasma, transmission of laser radiation through the target and plasma, as well as volume heating of the target material. It is experimentally determined that the laser energy conversion efficiency to X-rays with photon energies of a few kiloelectronvolts decreases with increasing target material density. With the use of targets of density 10 mg cm-3 this efficiency is two times lower in comparison to 2 mg cm-3 density targets. The duration and amplitude of laser pulses transmitted through the target decreases with increasing column target density (the product of target material density and its thickness). The spectra of ions emitted from low-density target plasmas are recorded using ion collectors positioned at different angles relative to the direction of laser beam propagation as well as a high-resolution Thomson mass spectrometer. The ion flux and ion energies are found to increase with increasing target material density. The peak of the ion energy spectrum is shifted towards higher energies with increasing laser radiation intensity.
Road simulation for four-wheel vehicle whole input power spectral density
Wang, Jiangbo; Qiang, Baomin
2017-05-01
As the vibration of running vehicle mainly comes from road and influence vehicle ride performance. So the road roughness power spectral density simulation has great significance to analyze automobile suspension vibration system parameters and evaluate ride comfort. Firstly, this paper based on the mathematical model of road roughness power spectral density, established the integral white noise road random method. Then in the MATLAB/Simulink environment, according to the research method of automobile suspension frame from simple two degree of freedom single-wheel vehicle model to complex multiple degrees of freedom vehicle model, this paper built the simple single incentive input simulation model. Finally the spectrum matrix was used to build whole vehicle incentive input simulation model. This simulation method based on reliable and accurate mathematical theory and can be applied to the random road simulation of any specified spectral which provides pavement incentive model and foundation to vehicle ride performance research and vibration simulation.
High power density reactors based on direct cooled particle beds
Powell, J. R.; Horn, F. L.
Reactors based on direct cooled High Temperature Gas Cooled Reactor (HTGR) type particle fuel are described. The small diameter particle fuel is packed between concentric porous cylinders to make annular fuel elements, with the inlet coolant gas flowing inwards. Hot exit gas flows out along the central channel of each element. Because of the very large heat transfer area in the packed beds, power densities in particle bed reactors (PBRs) are extremely high resulting in compact, lightweight systems. Coolant exit temperatures are high, because of the ceramic fuel temperature capabilities, and the reactors can be ramped to full power and temperature very rapidly. PBR systems can generate very high burst power levels using open cycle hydrogen coolant, or high continuous powers using closed cycle helium coolant. PBR technology is described and development requirements assessed.
Influence of motor unit firing statistics on the median frequency of the EMG power spectrum
van Boxtel, Anton; Schomaker, L R
1984-01-01
Changes in the EMG power spectrum during static fatiguing contractions are often attributed to changes in muscle fibre action potential conduction velocity. Mathematical models of the EMG power spectrum, which have been empirically confirmed, predict that under certain conditions a distinct maximum
The WiggleZ Dark Energy Survey: the selection function and z=0.6 galaxy power spectrum
Blake, Chris; Colless, Matthew; Couch, Warrick; Croom, Scott; Davis, Tamara; Drinkwater, Michael J; Forster, Karl; Glazebrook, Karl; Jelliffe, Ben; Jurek, Russell J; Li, I-hui; Madore, Barry; Martin, Chris; Pimbblet, Kevin; Poole, Gregory B; Pracy, Michael; Sharp, Rob; Wisnioski, Emily; Woods, David; Wyder, Ted
2010-01-01
We report one of the most accurate measurements of the three-dimensional large-scale galaxy power spectrum achieved to date, using 56,159 redshifts of bright emission-line galaxies at effective redshift z=0.6 from the WiggleZ Dark Energy Survey at the Anglo-Australian Telescope. We describe in detail how we construct the survey selection function allowing for the varying target completeness and redshift completeness. We measure the total power with an accuracy of approximately 5% in wavenumber bands of dk=0.01 h/Mpc. A model power spectrum including non-linear corrections, combined with a linear galaxy bias factor and a simple model for redshift-space distortions, provides a good fit to our data for scales k < 0.4 h/Mpc. The large-scale shape of the power spectrum is consistent with the best-fitting matter and baryon densities determined by observations of the Cosmic Microwave Background radiation. By splitting the power spectrum measurement as a function of tangential and radial wavenumbers we delineate t...
Selection of noise power ratio spectrum models for electronic measurement of the Boltzmann constant
Coakley, Kevin J
2016-01-01
In the electronic measurement of the Boltzmann constant based on Johnson noise thermometry, the ratio of the power spectral densities of thermal noise across a resistor and pseudo-random noise synthetically generated by a quantum-accurate voltage-noise source varies with frequency due to mismatch between transmission lines. We model this ratio spectrum as an even polynomial function of frequency. For any given frequency range, defined by the maximum frequency $f_{max}$, we select the optimal polynomial ratio spectrum model with a cross-validation method and estimate the conditional uncertainty of the constant term in the ratio spectrum model in a way that accounts for both random and systematic effects associated with imperfect knowledge of the model with a resampling method. We select $f_{max}$ by minimizing this conditional uncertainty. Since many values of $f_{max}$ yield conditional uncertainties close to the observed minimum value on a frequency grid, we quantify an additional component of uncertainty as...
Position-dependent power spectrum: a new observable in the large-scale structure
Chiang, Chi-Ting
2015-01-01
We present a new observable, position-dependent power spectrum, to measure the large-scale structure bispectrum in the squeezed configuration, where one wavenumber is much smaller than the other two. The squeezed-limit bispectrum measures how the small-scale power spectrum is modulated by a long-wavelength overdensity, which is due to gravitational evolution and possibly inflationary physics. We divide a survey into small subvolumes, compute the local power spectrum and the mean overdensity in each subvolume, and measure the correlation between them. The correlation measures the integral of the bispectrum, which is dominated by squeezed configurations if the scale of the local power spectrum is much smaller than the subvolume size. We use the separate universe approach to model how the small-scale power spectrum is affected by a long-wavelength overdensity gravitationally. This models the nonlinearity of the bispectrum better than the perturbation theory approach. Not only the new observable is easy to interp...
Model Independent Foreground Power Spectrum Estimation using WMAP 5-year Data
Ghosh, Tuhin; Jain, Pankaj; Souradeep, Tarun
2009-01-01
In this paper, we propose & implement on WMAP 5-year data, a model independent approach of foreground power spectrum estimation for multifrequency observations of CMB experiments. Recently a model independent approach of CMB power spectrum estimation was proposed by Saha et al. 2006. This methodology demonstrates that CMB power spectrum can be reliably estimated solely from WMAP data without assuming any template models for the foreground components. In the current paper, we extend this work to estimate the galactic foreground power spectrum using the WMAP 5 year maps following a self contained analysis. We apply the model independent method in harmonic basis to estimate the foreground power spectrum and frequency dependence of combined foregrounds. We also study the behaviour of synchrotron spectral index variation over different regions of the sky. We compare our results with those obtained from MEM foreground maps which are formed in pixel space. We find that relative to our model independent estimates...
The angular power spectrum of radio emission at 2.3 GHz
Giardino, G; Fosalba, P; Górski, K M; Jonas, J L; O'Mullane, W; Tauber, J A
2001-01-01
We have analysed the Rhodes/HartRAO survey at 2326 MHz and derived the global angular power spectrum of Galactic continuum emission. In order to measure the angular power spectrum of the diffuse component, point sources were removed from the map by median filtering. A least-square fit to the angular power spectrum of the entire survey with a power law spectrum C_l proportional to l^{-alpha}, gives alpha = 2.43 +/- 0.01 for l = 2-100. The angular power spectrum of radio emission appears to steepen at high Galactic latitudes and for observed regions with |b| > 20 deg, the fitted spectral index is alpha = 2.92 +/- 0.07. We have extrapolated this result to 30 GHz (the lowest frequency channel of Planck) and estimate that no significant contribution to the sky temperature fluctuation is likely to come from synchrotron at degree-angular scales
Power spectrum scale invariance identifies prefrontal dysregulation in paranoid schizophrenia.
Radulescu, Anca R; Rubin, Denis; Strey, Helmut H; Mujica-Parodi, Lilianne R
2012-07-01
Theory and experimental evidence suggest that complex living systems function close to the boundary of chaos, with erroneous organization to an improper dynamical range (too stiff or chaotic) underlying system-wide dysregulation and disease. We hypothesized that erroneous organization might therefore also characterize paranoid schizophrenia, via optimization abnormalities in the prefrontal-limbic circuit regulating emotion. To test this, we acquired fMRI scans from 35 subjects (N = 9 patients with paranoid schizophrenia and N = 26 healthy controls), while they viewed affect-valent stimuli. To quantify dynamic regulation, we analyzed the power spectrum scale invariance (PSSI) of fMRI time-courses and computed the geometry of time-delay (Poincaré) maps, a measure of variability. Patients and controls showed distinct PSSI in two clusters (k(1) : Z = 4.3215, P = 0.00002 and k(2) : Z = 3.9441, P = 0.00008), localized to the orbitofrontal/medial prefrontal cortex (Brodmann Area 10), represented by β close to white noise in patients (β ≈ 0) and in the pink noise range in controls (β ≈ -1). Interpreting the meaning of PSSI differences, the Poincaré maps indicated less variability in patients than controls (Z = -1.9437, P = 0.05 for k(1) ; Z = -2.5099, P = 0.01 for k(2) ). That the dynamics identified Brodmann Area 10 is consistent with previous schizophrenia research, which implicates this area in deficits of working memory, executive functioning, emotional regulation and underlying biological abnormalities in synaptic (glutamatergic) transmission. Our results additionally cohere with a large body of work finding pink noise to be the normal range of central function at the synaptic, cellular, and small network levels, and suggest that patients show less supple responsivity of this region.
Statistical characteristics of the observed Ly-α forest and the shape of initial power spectrum
Demiański, M.; Doroshkevich, A. G.; Turchaninov, V.
2003-04-01
Properties of approximately 4500 observed Ly α absorbers are investigated using the model of formation and evolution of dark matter (DM) structure elements based on the modified Zel'dovich theory. This model is generally consistent with simulations of absorber formation, describes the large-scale structure (LSS) observed in the galaxy distribution at small redshifts reasonably well and emphasizes the generic similarity of the LSS and absorbers. The simple physical model of absorbers asserts that they are composed of DM and gaseous matter. It allows us to estimate the column density and overdensity of DM and gaseous components and the entropy of the gas trapped within the DM potential wells. The parameters of the DM component are found to be consistent with theoretical expectations for the Gaussian initial perturbations with the warm dark matter-like power spectrum. The basic physical factors responsible for the evolution of the absorbers are discussed. The analysis of redshift distribution of absorbers confirms the self-consistency of the adopted physical model, Gaussianity of the initial perturbations and allows one to estimate the shape of the initial power spectrum at small scales that, in turn, restricts the mass of the dominant fraction of DM particles to MDM>= 1.5-5 keV. Our results indicate a possible redshift variations of intensity of the ultraviolet background by approximately a factor of 2-3 at redshifts z~ 2-3.
Maximum flux density of the gyrosynchrotron spectrum in a nonuniform source
Institute of Scientific and Technical Information of China (English)
Ai-Hua Zhou; Rong-Chuan Wang; Cheng-Wen Shao
2009-01-01
The maximum flux density of a gyrosynchrotron radiation spectrum in a mag- netic dip|oe model with self absorption and gyroresonance is calculated. Our calculations show that the maximum flux density of the gyrosynchrotron spectrum increases with in- creasing low-energy cutoff, number density, input depth of energetic electrons, magnetic field strength and viewing angle, and with decreasing energy spectral index of energetic electrons, number density and temperature of thermal electrons. It is found that there are linear correlations between the logarithms of the maximum flux density and the above eight parameters with correlation coefficients higher than 0.91 and fit accuracies better than 10%. The maximum flux density could be a good indicator of the changes of these source parameters. In addition, we find that there are very good positive linear correla- tions between the logarithms of the maximum flux density and peak frequency when the above former five parameters vary respectively. Their linear correlation coefficients are higher than 0.90 and the fit accuracies are better than 0.5%.
Magnetocaloric Materials and the Optimization of Cooling Power Density
Wikus, Patrick; Canavan, Edgar; Heine, Sarah Trowbridge; Matsumoto, Koichi; Numazawa, Takenori
2014-01-01
The magnetocaloric effect is the thermal response of a material to an external magnetic field. This manuscript focuses on the physics and the properties of materials which are commonly used for magnetic refrigeration at cryogenic temperatures. After a brief overview of the magnetocaloric effect and associated thermodynamics, typical requirements on refrigerants are discussed from a standpoint of cooling power density optimization. Finally, a compilation of the most important properties of several common magnetocaloric materials is presented.
Probability density function modeling for sub-powered interconnects
Pater, Flavius; Amaricǎi, Alexandru
2016-06-01
This paper proposes three mathematical models for reliability probability density function modeling the interconnect supplied at sub-threshold voltages: spline curve approximations, Gaussian models,and sine interpolation. The proposed analysis aims at determining the most appropriate fitting for the switching delay - probability of correct switching for sub-powered interconnects. We compare the three mathematical models with the Monte-Carlo simulations of interconnects for 45 nm CMOS technology supplied at 0.25V.
Power spectral density in balance assessment. Description of methodology.
Syczewska, Małgorzata; Zielińska, Teresa
2010-01-01
One of the methods used in clinical setting to assess the balance function is the measurement of the centre of pressure trajectory (COP). The COP trajectory is strongly dependent on the body centre of mass trajectory (COM), but in case of balance problems the corrective signals influence this dependence. The aim of the present study is to explore the possibility of using power spectral density function of the COP vs. COM signal in assessing the amount of correction signals. As the aim was a methodological one, only one healthy adult subject participated in the study. This subject performed five balance tasks of increasing difficulty. The COP trajectory was recorded using the Kistler force plate, and COM trajectory was calculated based on the marker trajectories placed on the subject's body and simultaneously recorded with VICON 460 system. The COM data were subtracted from COP trajectory in anteroposterior (AP) and lateral direction. Next the power spectral density (PSD) was calculated for the new signals. The power spectral density is very low for easiest condition, but increases with the difficulty of task. Moreover, it also provides information in which plane (sagittal or frontal) more correction movements are needed to maintain stability.
Proton Stopping Power of Different Density Profile Plasmas
Casas, David; Andreev, Alexander A; Schnürer, Matthias; Morales, Roberto
2014-01-01
In this work, the stopping power of a partially ionized plasma is analyzed by means of free electron stopping and bound electron stopping. For the first one, the RPA dielectric function is used, and for the latter one, an interpolation of high and low projectile velocity formulas is used. The dynamical energy loss of an ion beam inside a plasma is estimated by using an iterative scheme of calculation. The Abel inversion is also applied when we have a plasma with radial symmetry. Finally, we compare our methods with two kind of plasmas. In the first one, we estimate the energy loss in a plasma created by a laser prepulse, whose density is approximated by a piecewise function. For the latter one, a radial electron density is supposed and the stopping is obtained as function of radius from the calculated lateral points. In both cases, the dependence with the density profile is observed.
PROTON STOPPING POWER OF DIFFERENT DENSITY PROFILE PLASMAS
Directory of Open Access Journals (Sweden)
David Casas
2015-04-01
Full Text Available In this work, the stopping power of a partially ionized plasma is analyzed by means of free electron stopping and bound electron stopping. For the first instance, the RPA dielectric function is used, and for the latter one, an interpolation of high and low projectile velocity formulas is used. The dynamical energy loss of a ion beam inside a plasma is estimated by using an iterative scheme of calculation. The Abel inversion is also applied when we have a plasma with radial symmetry. Finally, we compare our methods with two kind of plasmas. In the first one, we estimate the energy loss in a plasma created by a laser prepulse, whose density is approximated by a piecewise function. For the latter one, a radial electron density is supposed and the stopping is obtained as a function of radius from the calculated lateral points. In both cases, the dependence with the density profile is observed.
Fuel rod behavior under normal operating conditions in Super Fast Reactor with high power density
Energy Technology Data Exchange (ETDEWEB)
Ju, Haitao, E-mail: haitaoju@gmail.com [Science and Technology on Reactor System Design Technology Laboratory, Chengdu, Sichuan 610041 (China); Ishiwatari, Yuki [Department of Nuclear Engineering and Management, The University of Tokyo, Hongo, Bunkyo, Tokyo 113-8656 (Japan); Oka, Yoshiaki [Joint Department of Nuclear Energy, Waseda University, Totsukamachi, Shinjuku, Tokyo 169-8050 (Japan)
2015-08-15
Highlights: • The improved core of Super Fast Reactor with high power density is analyzed. • We analyzed four types of the limiting fuel rods. • The influence of Pu enrichment and compressive stress to yield strength ratio are analyzed. • The improved fuel rod design of the new core is suggested. - Abstract: A Super Fast Reactor is a pressure-vessel type, fast spectrum SuperCritical Water Reactor (SCWR) which is presently researched in a Japanese project. A preliminary core has an average power density of 158.8 W/cc. However one of the most important advantages of the Super Fast Reactor is the higher power density compared to the thermal spectrum SCWR, which reduces the capital cost. After the sensitivity analyses on the fuel rod configurations, the fuel assembly configurations and the core configurations, an improved core with an average power density of 294.8 W/cc is designed by 3-D neutronic/thermal-hydraulic coupled calculations. In order to ensure the fuel rod integrity of new core design with high power density, the fuel rod behaviors under normal operating condition are analyzed using fuel performance code FEMAXI-6. The power histories of each fuel rod are taken from the neutronics calculation results in the core design. The cladding surface temperature histories are generated from the thermal-hydraulic calculation results in the core design. Four types of the limiting fuel rods, individually with the Maximum Cladding Surface Temperature (MCST), Maximum Power Peak (MPP), Maximum Discharge Burnup (MDB) and Different Coolant Flow Pattern (DCFP), are chosen to cover all the fuel rods in the core. The available design range of the fuel rod design parameters, such as initial gas plenum pressure, gas plenum position, gas plenum length, grain size and gap size, are found out in order to satisfy the following design criteria: (1) Maximum fuel centerline temperature should be less than 1900 °C. (2) Maximum cladding stress in circumferential direction should
Zessin, H.; Spies, P.; Mateu, L.
2016-11-01
In this study, we report a power management circuit for a combined piezoelectric- electrodynamic generator. A piezoelectric element is bonded to a spring steel cantilever beam and a magnet, used as tip mass, oscillates through a coil. This principle creates the combined generator. A test setup has been created to automate the characterization of the piezoelectric generator and its power management circuit. Three different power management circuits for the piezoelectric part of the combined generator have been analysed: a bridge rectifier, an SSHI circuit with an external inductance and an SSHI circuit which utilizes the coil of the electrodynamic generator as circuit element. The three circuits are compared in terms of their output power, efficiency and power density. The SSHI circuit with an external inductance has the highest output power and efficiency, followed by the SSHI circuit with the electrodynamic generator coil. The power density of the bridge rectifier is the highest but for higher efficiency the power density of the SSHI circuit with the coil of the electromagnetic generator reaches the best results.
First results from the Very Small Array -- III. The CMB power spectrum
2002-01-01
We present the power spectrum of the fluctuations in the cosmic microwave background detected by the Very Small Array (VSA) in its first season of observations in its compact configuration. We find clear detections of first and second acoustic peaks at l~200 and l~550, plus detection of power on scales up to l=800. The VSA power spectrum is in very good agreement with the results of the Boomerang, Dasi and Maxima telescopes despite the differing potential systematic errors.
Crossover in the power spectrum of a driven diffusive lattice-gas model
DEFF Research Database (Denmark)
Andersen, Jørgen Vitting; Jensen, Henrik Jeldtoft; Mouritsen, Ole G.
1991-01-01
A driven diffusive lattice-gas model with stochastic dynamics is used to study, via a Monte Carlo simulation, the fluctuations in the particle density and the lifetime of the particles in the system. The scaling properties of the power spectrum S(f) and the lifetime distribution function D......(t) exhibit a crossover from (1/f3)- to (1/f2)-noise behavior, with β≃1.5, when the drive is sufficiently strong to induce a characteristic time scale. We argue that the scaling behavior with β≃1.5 is governed by the stochastic nature of the dynamics whereas deterministic dynamics leads to β≃1....
Statistical characteristics of observed Ly-$\\alpha$ forest and the shape of initial power spectrum
Demianski, M
2002-01-01
Properties of $\\sim$ 5000 observed Ly-$\\alpha$ absorbers are investigated using the model of formation and evolution of DM structure elements based on the Zel'dovich theory. This model is generally consistent with simulations of absorbers formation, accurately describes the Large Scale Structure observed in the galaxy distribution at small redshifts and emphasizes the generic similarity of the LSS and absorbers. The simple physical model of absorbers asserts that they are composed of DM and gaseous matter and it allows us to estimate the column density and overdensity of DM and gaseous components and the entropy of the gas trapped within the DM potential wells. The parameters of DM component are found to be consistent with theoretical expectations for the Gaussian initial perturbations with the WDM--like power spectrum. We demonstrate the influence of the main physical factors responsible for the absorbers evolution. The analysis of redshift distribution of absorbers confirms the self consistence of the assum...
The power spectrum and bispectrum of SDSS DR11 BOSS galaxies II: cosmological interpretation
Gil-Marín, Héctor; Noreña, Jorge; Cuesta, Antonio J; Samushia, Lado; Percival, Will J; Wagner, Christian; Manera, Marc; Schneider, Donald P
2014-01-01
We examine the cosmological implications of the measurements of the linear growth rate of cosmological structure obtained in a companion paper from the power spectrum and bispectrum monopoles of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey Data, Release 11, CMASS galaxies. This measurement was of $f^{0.43}\\sigma_8$, where $\\sigma_8$ is the amplitude of dark matter density fluctuations, and $f$ is the linear growth rate, at the effective redshift of the survey, $z_{\\rm eff}=0.57$. In conjunction with Cosmic Microwave Background (CMB) data, interesting constraints can be placed on models with non-standard neutrino properties and models where gravity deviates from general relativity on cosmological scales. In particular, the sum of the masses of the three species of the neutrinos is constrained to $m_\
Reheating Effects in the Matter Power Spectrum and Implications for Substructure
Erickcek, Adrienne L
2011-01-01
The thermal and expansion history of the Universe before big bang nucleosynthesis is unknown. We investigate the evolution of cosmological perturbations through the transition from an early matter era to radiation domination. We treat reheating as the perturbative decay of an oscillating scalar field into relativistic plasma and cold dark matter. After reheating, we find that subhorizon perturbations in the decay-produced dark matter density are significantly enhanced, while subhorizon radiation perturbations are instead suppressed. If dark matter originates in the radiation bath after reheating, this suppression may be the primary cut-off in the matter power spectrum. Conversely, for dark matter produced non-thermally from scalar decay, enhanced perturbations can drive structure formation during the cosmic dark ages and dramatically increase the abundance of compact substructures. For low reheat temperatures, we find that as much as 50% of all dark matter is in microhalos with M > 0.1 Earth masses at z=100, ...
Daniell method for power spectral density estimation in atomic force microscopy
Energy Technology Data Exchange (ETDEWEB)
Labuda, Aleksander [Asylum Research an Oxford Instruments Company, Santa Barbara, California 93117 (United States)
2016-03-15
An alternative method for power spectral density (PSD) estimation—the Daniell method—is revisited and compared to the most prevalent method used in the field of atomic force microscopy for quantifying cantilever thermal motion—the Bartlett method. Both methods are shown to underestimate the Q factor of a simple harmonic oscillator (SHO) by a predictable, and therefore correctable, amount in the absence of spurious deterministic noise sources. However, the Bartlett method is much more prone to spectral leakage which can obscure the thermal spectrum in the presence of deterministic noise. By the significant reduction in spectral leakage, the Daniell method leads to a more accurate representation of the true PSD and enables clear identification and rejection of deterministic noise peaks. This benefit is especially valuable for the development of automated PSD fitting algorithms for robust and accurate estimation of SHO parameters from a thermal spectrum.
The visibility based Tapered Gridded Estimator (TGE) for the redshifted 21-cm power spectrum
Choudhuri, Samir; Chatterjee, Suman; Ali, Sk Saiyad; Roy, Nirupam; Ghosh, Abhik
2016-01-01
We present the improved visibility based Tapered Gridded Estimator (TGE) for the power spectrum of the diffuse sky signal. The visibilities are gridded to reduce the computation, and tapered through a convolution to suppress the contribution from the outer regions of the telescope's field of view. The TGE also internally estimates the noise bias, and subtracts this out to give an unbiased estimate of the power spectrum. An earlier version of the 2D TGE for the angular power spectrum $C_{\\ell}$ is improved and then extended to obtain the 3D TGE for the power spectrum $P({\\bf k})$ of the 21-cm brightness temperature fluctuations. Analytic formulas are also presented for predicting the variance of the binned power spectrum. The estimator and its variance predictions are validated using simulations of $150 \\, {\\rm MHz}$ GMRT observations. We find that the estimator accurately recovers the input model for the 1D Spherical Power Spectrum $P(k)$ and the 2D Cylindrical Power Spectrum $P(k_\\perp,k_\\parallel)$, and the...
Liquid lithium for high power density fragmentation targets
Nolen, J. A.; Reed, C. B.; Hassanein, A.; Morrissey, D. J.; Ottarson, J. H.; Sherrill, B. M.
2001-10-01
Windowless liquid lithium targets for in-flight fragmentation or fission of high power heavy ion beams are being developed for the U.S. RIA project. With uranium beam power of 100 kW and a beam spot diameter of 1 mm the power density in the target is over 1 MW/cm3. Thermal analysis for this example indicates a very low peak temperature for the lithium when flowing at a linear velocity of 10 m/s. A vacuum test chamber is under construction at Argonne at an existing liquid lithium facility to demonstrate a 2 cm thick windowless target. As a first step towards using liquid lithium target technology at a nuclear physics fragmentation facility, a lower power target is being constructed for use at the NSCL. This target will use beryllium windows with flowing lithium. It is designed for beams between oxygen and calcium with beam power above 3 kW. The tapered beryllium windows are each 1 mm thick for the calcium beams and 7 mm thick for the oxygen beams. The lithium is 5 mm thick. This gives an overall target thickness ranging from about 1 g/cm2 to 3 g/cm2 which is adjusted by moving the target vertically. The designs of these targets and the status of the prototypes will be discussed.
Primordial black holes do not (yet) constrain the primordial power spectrum
Akrami, Yashar; Sandstad, Marit
2016-01-01
Primordial black holes (PBHs) are thought to have formed from extremely overdense regions that reentered the horizon after the end of inflation if there was sufficient power in primordial perturbations on specific scales. The existence (and abundance) of PBHs is therefore governed by the inflationary power spectrum. So far no primordial black holes have been observed, and instead, increasingly stringent bounds on their existence at different scales have been set. Up until recently this has been exploited in attempts to constrain parts of the inflationary power spectrum that are unconstrained by the cosmic microwave background and other cosmological observations. In this letter we point out that this simple translation of the PBH constraints into constraints on the primordial power spectrum is inaccurate as it fails to take into account realistic aspects of the PBH formation and evolution process. We show this by displaying a concrete example of a power spectrum that is seemingly in conflict with the constrain...
Liang, B.; Iwnicki, S. D.; Zhao, Y.
2013-08-01
The power spectrum is defined as the square of the magnitude of the Fourier transform (FT) of a signal. The advantage of FT analysis is that it allows the decomposition of a signal into individual periodic frequency components and establishes the relative intensity of each component. It is the most commonly used signal processing technique today. If the same principle is applied for the detection of periodicity components in a Fourier spectrum, the process is called the cepstrum analysis. Cepstrum analysis is a very useful tool for detection families of harmonics with uniform spacing or the families of sidebands commonly found in gearbox, bearing and engine vibration fault spectra. Higher order spectra (HOS) (also known as polyspectra) consist of higher order moment of spectra which are able to detect non-linear interactions between frequency components. For HOS, the most commonly used is the bispectrum. The bispectrum is the third-order frequency domain measure, which contains information that standard power spectral analysis techniques cannot provide. It is well known that neural networks can represent complex non-linear relationships, and therefore they are extremely useful for fault identification and classification. This paper presents an application of power spectrum, cepstrum, bispectrum and neural network for fault pattern extraction of induction motors. The potential for using the power spectrum, cepstrum, bispectrum and neural network as a means for differentiating between healthy and faulty induction motor operation is examined. A series of experiments is done and the advantages and disadvantages between them are discussed. It has been found that a combination of power spectrum, cepstrum and bispectrum plus neural network analyses could be a very useful tool for condition monitoring and fault diagnosis of induction motors.
Protostellar fragmentation in a power-law density distribution
Burkert, A; Bodenheimer, P
1997-01-01
Hydrodynamical calculations in three space dimensions of the collapse of an isothermal, rotating 1 M\\sol protostellar cloud are presented. The initial density stratification is a power law with density $\\rho \\propto r^{-p}$, with $p=1$. The case of the singular isothermal sphere ($p=2$) is not considered; however $p=1$ has been shown observationally to be a good representation of the density distribution in molecular cloud cores just before the beginning of collapse. The collapse is studied with two independent numerical methods, an SPH code with 200,000 particles, and a finite-difference code with nested grids which give high spatial resolution in the inner regions. Although previous numerical studies have indicated that such a power-law distribution would not result in fragmentation into a binary system, both codes show, in contrast, that multiple fragmentation does occur in the central regions of the protostar. Thus the process of binary formation by fragmentation is shown to be consistent with the fact th...
Assessment of Microbial Fuel Cell Configurations and Power Densities
Logan, Bruce E.
2015-07-30
Different microbial electrochemical technologies are being developed for a many diverse applications, including wastewater treatment, biofuel production, water desalination, remote power sources, and as biosensors. Current and energy densities will always be limited relative to batteries and chemical fuel cells, but these technologies have other advantages based on the self-sustaining nature of the microorganisms that can donate or accept electrons from an electrode, the range of fuels that can be used, and versatility in the chemicals that can be produced. The high cost of membranes will likely limit applications of microbial electrochemical technologies that might require a membrane. For microbial fuel cells, which do not need a membrane, questions remain on whether larger-scale systems can produce power densities similar to those obtained in laboratory-scale systems. It is shown here that configuration and fuel (pure chemicals in laboratory media versus actual wastewaters) remain the key factors in power production, rather than the scale of the application. Systems must be scaled up through careful consideration of electrode spacing and packing per unit volume of reactor.
Relativistic Corrections to the Thermal Sunyaev-Zel'dovich Power Spectrum
Institute of Scientific and Technical Information of China (English)
Hai-Ning Li
2003-01-01
We present a quantitative estimate of the relativistic corrections to the thermal SZ power spectrum produced by the energetic electrons in massive clusters. The corrections are well within 10% for current experiments with working frequencies below v ＜ 100 GHz, but become non-negligible at high frequencies v ＞350 GHz. Moreover, the corrections appear to be slightly smaller at higher e or smaller angular scales. We conclude that there is no need to include the relativistic corrections in the theoretical study of the SZ power spectrum especially at low frequencies unless the SZ power spectrum is used for precision cosmology.
Correlation between the Flux Density and Polarization for Flat Spectrum Radio Quasars
Indian Academy of Sciences (India)
Fei-Peng Pi; Yong-Xiang Wang; Jing Pan
2011-03-01
In this paper, using the preliminary database of the University of Michigan Radio Astronomy Observatory (UMRAO) at the radio frequencies, we calculated the weighted polarization at 8 GHz and investigated the correlation between the polarization and the flux density for 92 flat spectrum radio quasars (FSRQs). We found that the two observations are closely and positively correlated for FSRQs. This is perhaps from a relativistic beaming effect.
Complex spectrum of finite-density lattice QCD with static quarks at strong coupling
Nishimura, Hiromichi; Pangeni, Kamal
2015-01-01
We calculate the spectrum of transfer matrix eigenvalues associated with Polyakov loops in finite-density lattice QCD with static quarks. These eigenvalues determine the spatial behavior of Polyakov loop correlations functions. Our results are valid for all values of the gauge coupling in $1+1$ dimensions, and valid in the strong-coupling region for any number of dimensions. When the quark chemical potential $\\mu$ is nonzero, the spatial transfer matrix $T$ is non-Hermitian. The appearance of complex eigenvalues in $T$ is a manifestation of the sign problem in finite-density QCD. The invariance of finite-density QCD under the combined action of charge conjugation $\\mathcal{C}$ and complex conjugation $\\mathcal{K}$ implies that the eigenvalues of $T$ are either real or part of a complex pair. Calculation of the spectrum confirms the existence of complex pairs in much of the temperature-chemical potential plane. Many features of the spectrum for static quarks are determined by a particle-hole symmetry. For $\\mu...
Flexible and Lightweight Fuel Cell with High Specific Power Density.
Ning, Fandi; He, Xudong; Shen, Yangbin; Jin, Hehua; Li, Qingwen; Li, Da; Li, Shuping; Zhan, Yulu; Du, Ying; Jiang, Jingjing; Yang, Hui; Zhou, Xiaochun
2017-06-27
Flexible devices have been attracting great attention recently due to their numerous advantages. But the energy densities of current energy sources are still not high enough to support flexible devices for a satisfactory length of time. Although proton exchange membrane fuel cells (PEMFCs) do have a high-energy density, traditional PEMFCs are usually too heavy, rigid, and bulky to be used in flexible devices. In this research, we successfully invented a light and flexible air-breathing PEMFC by using a new design of PEMFC and a flexible composite electrode. The flexible air-breathing PEMFC with 1 × 1 cm(2) working area can be as light as 0.065 g and as thin as 0.22 mm. This new PEMFC exhibits an amazing specific volume power density as high as 5190 W L(-1), which is much higher than traditional (air-breathing) PEMFCs. Also outstanding is that the flexible PEMFC retains 89.1% of its original performance after being bent 600 times, and it retains its original performance after being dropped five times from a height of 30 m. Moreover, the research has demonstrated that when stacked, the flexible PEMFCs are also useful in mobile applications such as mobile phones. Therefore, our research shows that PEMFCs can be made light, flexible, and suitable for applications in flexible devices. These innovative flexible PEMFCs may also notably advance the progress in the PEMFC field, because flexible PEMFCs can achieve high specific power density with small size, small volume, low weight, and much lower cost; they are also much easier to mass produce.
A New Hard Switching Bidirectional Converter With High Power Density
Directory of Open Access Journals (Sweden)
Bahador Fani
2010-01-01
Full Text Available In this paper, a new isolated dc-dc bidirectional converter is proposed. This converter consists of two transformers (flyback and forward and only one switch in primary side and one switch in secondary side of transformers. In this converter energy transfers to the output in both on and off switch states so power density of this converter is high This converter controlled by PWM signal. Also this converter operates over a wide input voltage range. Theoretical analysis is presented and computer simulation and experimental results verify the converter analysis.
Wind tunnel study of the power output spectrum in a micro wind farm
Bossuyt, Juliaan; Howland, Michael F.; Meneveau, Charles; Meyers, Johan
2016-09-01
Instrumented small-scale porous disk models are used to study the spectrum of a surrogate for the power output in a micro wind farm with 100 models of wind turbines. The power spectra of individual porous disk models in the first row of the wind farm show the expected -5/3 power law at higher frequencies. Downstream models measure an increased variance due to wake effects. Conversely, the power spectrum of the sum of the power over the entire wind farm shows a peak at the turbine-to-turbine travel frequency between the model turbines, and a near -5/3 power law region at a much wider range of lower frequencies, confirming previous LES results. Comparison with the spectrum that would result when assuming that the signals are uncorrelated, highlights the strong effects of correlations and anti-correlations in the fluctuations at various frequencies.
Observability of secondary Doppler peaks in the CMBR power spectrum by experiments with small fields
Hobson, M P; Magueijo, Joao
1996-01-01
We investigate the effects of finite sky coverage on the spectral resolution \\Delta\\ell in the estimation of the CMBR angular power spectrum C^{\\ell}. A method is developed for obtaining quasi-independent estimates of the power spectrum, and the cosmic/sample variance of these estimates is calculated. The effect of instrumental noise is also considered for prototype interferometer and single-dish experiments. By proposing a statistic for the detection of secondary (Doppler) peaks in the CMBR power spectrum, we then compute the significance level at which such peaks may be detected for a large range of model CMBR experiments. In particular, we investigate experimental design features required to distinguish between competing cosmological theories, such as cosmic strings and inflation, by establishing whether or not secondary peaks are present in the CMBR power spectrum.
Statistical characteristics of the observed Lyα forest and the shape of the initial power spectrum
Demiański, M.; Doroshkevich, A. G.; Turchaninov, V. I.
2006-09-01
We analyse the basic properties of about 6000 Lyman α absorbers observed in the high-resolution spectra of 19 quasars. We compare their observed characteristics with the predictions of our model of formation and evolution of absorbers and dark matter (DM) pancakes and voids based on the Zel'dovich theory of gravitational instability. This model asserts that absorbers are formed in the course of both linear and non-linear adiabatic and shock compression of DM and gaseous matter. Our model is consistent with simulations of structure formation, describes reasonably well the large-scale structure (LSS) observed in the distribution of galaxies at small redshifts, and emphasizes the generic similarity of the process of formation of LSS and absorbers. Using this model, we are able to link the column density and overdensity of the DM and gaseous components with the observed column density of neutral hydrogen, redshifts and Doppler parameters of absorbers. We show that the colder absorbers are associated with rapidly expanded underdense regions of galactic scale. We extend an existing method of measuring the power spectrum of initial perturbations. The observed separations between absorbers and their DM column density are linked with the correlation function of the initial velocity field. Applying this method to our sample of absorbers, we recover the cold dark matter (CDM) like power spectrum at scales of 10h-1 >= D >= 0.15h-1Mpc with a precision of ~15 per cent. However, at scales of ~3-150h-1kpc, the measured and CDM-like spectra are different. This result suggests a possible complex inflation with generation of excess power at small scales. Both confirmation of the CDM-like shape of the initial power spectrum and detection of its distortions at small scales are equally important for the widely discussed problems of physics of the early Universe, galaxy formation, and reheating of the Universe.
Individual power density spectra of Swift gamma-ray bursts
Guidorzi, C; Amati, L
2016-01-01
Timing analysis is a powerful tool with which to shed light on the still obscure emission physics and geometry of the prompt emission of GRBs. Fourier power density spectra (PDS) characterise time series as stochastic processes and can be used to search for coherent pulsations and to investigate the dominant variability timescales. Because of the limited duration and of the statistical properties, modelling the PDS of individual GRBs is challenging, and only average PDS of large samples have been discussed in the literature. We characterise the individual PDS of GRBs in terms of a stochastic process, and carry out for the first time a systematic search for periodic signals and for a link between the PDS and other observables. We present a Bayesian procedure that uses a Markov chain Monte Carlo technique and apply it to study 215 bright long GRBs detected with the Swift Burst Alert Telescope from January 2005 to May 2015. The PDS are modelled with a power-law either with or without a break. Two classes of GRBs...
Statistical connection of peak counts to power spectrum and moments in weak-lensing field
Shirasaki, Masato
2017-02-01
The number density of local maxima of weak-lensing field, referred to as weak-lensing peak counts, can be used as a cosmological probe. However, its relevant cosmological information is still unclear. We study the relationship between the peak counts and other statistics in weak-lensing field by using 1000 ray-tracing simulations. We construct a local transformation of lensing field K to a new Gaussian field y, named local-Gaussianized transformation. We calibrate the transformation with numerical simulations so that the one-point distribution and the power spectrum of K can be reproduced from a single Gaussian field y and monotonic relation between y and K. Therefore, the correct information of two-point clustering and any order of moments in weak-lensing field should be preserved under local-Gaussianized transformation. We then examine if local-Gaussianized transformation can predict weak-lensing peak counts in simulations. The local-Gaussianized transformation is insufficient to explain weak-lensing peak counts in the absence of shape noise. The prediction by local-Gaussianized transformation underestimates the simulated peak counts with a level of ˜20-30 per cent over a wide range of peak heights. Local-Gaussianized transformation can predict the weak-lensing peak counts with an ˜10 per cent accuracy in the presence of shape noise. Our analyses suggest that the cosmological information beyond power spectrum and its moments would be necessary to predict the weak-lensing peak counts with a percent-level accuracy, which is an expected statistical uncertainty in upcoming wide-field galaxy surveys.
Roy, A; Arzoumanian, D; Peretto, N; Palmeirim, P; Konyves, V; Schneider, N; Benedettini, M; Di Francesco, J; Elia, D; Hill, T; Ladjelate, B; Louvet, F; Motte, F; Pezzuto, S; Schisano, E; Shimajiri, Y; Spinoglio, L; Ward-Thompson, D; White, G
2015-01-01
Two major features of the prestellar CMF are: 1) a broad peak below 1 Msun, presumably corresponding to a mean gravitational fragmentation scale, and 2) a characteristic power-law slope, very similar to the Salpeter slope of the stellar initial mass function (IMF) at the high-mass end. While recent Herschel observations have shown that the peak of the prestellar CMF is close to the thermal Jeans mass in marginally supercritical filaments, the origin of the power-law tail of the CMF/IMF at the high-mass end is less clear. Inutsuka (2001) proposed a theoretical scenario in which the origin of the power-law tail can be understood as resulting from the growth of an initial spectrum of density perturbations seeded along the long axis of filaments by interstellar turbulence. Here, we report the statistical properties of the line-mass fluctuations of filaments in nearby molecular clouds observed with Herschel using a 1-D power spectrum analysis. The observed filament power spectra were fitted by a power-law function...
Power spectrum analysis of ionospheric fluctuations with the Murchison Widefield Array
Loi, Shyeh Tjing; Murphy, Tara; Cairns, Iver H; Bell, Martin; Hurley-Walker, Natasha; Morgan, John; Lenc, Emil; Offringa, A R; Feng, L; Hancock, P J; Kaplan, D L; Kudryavtseva, N; Bernardi, G; Bowman, J D; Briggs, F; Cappallo, R J; Corey, B E; Deshpande, A A; Emrich, D; Gaensler, B M; Goeke, R; Greenhill, L J; Hazelton, B J; Johnston-Hollitt, M; Kasper, J C; Kratzenberg, E; Lonsdale, C J; Lynch, M J; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Oberoi, D; Ord, S M; Prabu, T; Rogers, A E E; Roshi, A; Shankar, N Udaya; Srivani, K S; Subrahmanyan, R; Tingay, S J; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L
2015-01-01
Low-frequency, wide field-of-view (FoV) radio telescopes such as the Murchison Widefield Array (MWA) enable the ionosphere to be sampled at high spatial completeness. We present the results of the first power spectrum analysis of ionospheric fluctuations in MWA data, where we examined the position offsets of radio sources appearing in two datasets. The refractive shifts in the positions of celestial sources are proportional to spatial gradients in the electron column density transverse to the line of sight. These can be used to probe plasma structures and waves in the ionosphere. The regional (10-100 km) scales probed by the MWA, determined by the size of its FoV and the spatial density of radio sources (typically thousands in a single FoV), complement the global (100-1000 km) scales of GPS studies and local (0.01-1 km) scales of radar scattering measurements. Our data exhibit a range of complex structures and waves. Some fluctuations have the characteristics of travelling ionospheric disturbances (TIDs), whi...
Dikmese, Sener; Srinivasan, Sudharsan; Shaat, Musbah; Bader, Faouzi; Renfors, Markku
2014-12-01
Multicarrier waveforms have been commonly recognized as strong candidates for cognitive radio. In this paper, we study the dynamics of spectrum sensing and spectrum allocation functions in cognitive radio context using very practical signal models for the primary users (PUs), including the effects of power amplifier nonlinearities. We start by sensing the spectrum with energy detection-based wideband multichannel spectrum sensing algorithm and continue by investigating optimal resource allocation methods. Along the way, we examine the effects of spectral regrowth due to the inevitable power amplifier nonlinearities of the PU transmitters. The signal model includes frequency selective block-fading channel models for both secondary and primary transmissions. Filter bank-based wideband spectrum sensing techniques are applied for detecting spectral holes and filter bank-based multicarrier (FBMC) modulation is selected for transmission as an alternative multicarrier waveform to avoid the disadvantage of limited spectral containment of orthogonal frequency-division multiplexing (OFDM)-based multicarrier systems. The optimization technique used for the resource allocation approach considered in this study utilizes the information obtained through spectrum sensing and knowledge of spectrum leakage effects of the underlying waveforms, including a practical power amplifier model for the PU transmitter. This study utilizes a computationally efficient algorithm to maximize the SU link capacity with power and interference constraints. It is seen that the SU transmission capacity depends critically on the spectral containment of the PU waveform, and these effects are quantified in a case study using an 802.11-g WLAN scenario.
Han, Jiang-An; Kong, Zhi-Hui; Ma, Kaixue; Yeo, Kiat Seng; Lim, Wei Meng
2016-11-01
This paper presents a novel balun for a millimeter-wave power amplifier (PA) design to achieve high-power density in a 65-nm low-power (LP) CMOS process. By using a concentric winding technique, the proposed parallel combining balun with compact size accomplishes power combining and unbalance-balance conversion concurrently. For calculating its power combination efficiency in the condition of various amplitude and phase wave components, a method basing on S-parameters is derived. Based on the proposed parallel combining balun, a fabricated 60-GHz industrial, scientific, and medical (ISM) band PA with single-ended I/O achieves an 18.9-dB gain and an 8.8-dBm output power at 1-dB compression and 14.3-dBm saturated output power ( P sat) at 62 GHz. This PA occupying only a 0.10-mm2 core area has demonstrated a high-power density of 269.15 mW/mm2 in 65 nm LP CMOS.
Probing reionization with the cross power spectrum of 21 cm and near-infrared radiation backgrounds
Mao, Xiao-Chun
2014-01-01
The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared (NIR) background light from the high-redshift galaxies promises to be a powerful probe of cosmic reionization. In this paper, we investigate the cross power spectrum during the epoch of reionization. We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model: metal-free stars and metal-poor stars. The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements. Then the intensity of NIR background is estimated by collecting emission from stars in the first-light galaxies. On large scales, we find the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization. However, these two radiation backgrounds quickly become anti-correlated as reionization proceeds. The maximum absolut...
The Sunyaev-Zel'dovich angular power spectrum as a probe of cosmological parameters
Komatsu, E; Komatsu, Eiichiro; Seljak, Uros
2002-01-01
The angular power spectrum of the SZ effect, C_l, is a powerful probe of cosmology. It is easier to detect than individual clusters in the field, is insensitive to observational selection effects and does not require a calibration between cluster mass and flux, reducing the systematic errors which dominate the cluster-counting constraints. It receives a dominant contribution from cluster region between 20-40% of the virial radius and is thus insensitive to the poorly known gas physics in the cluster centre, such as cooling or (pre)heating. In this paper we derive a refined analytic prediction for C_l using the universal gas-density and temperature profile and the dark-matter halo mass function. The predicted C_l has no free parameters and fits all of the published hydrodynamic simulation results to better than a factor of two around l=3000. We find that C_l scales as (sigma_8)^7 times (Omega_b h)^2 and is almost independent of all of the other cosmological parameters. This differs from the local cluster abund...
First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations Angular Power Spectrum
Hinshaw, G; Verde, L; Hill, R S; Meyer, S S; Barnes, C; Bennett, C L; Halpern, M; Jarosik, N C; Kogut, A J; Komatsu, E; Limon, M; Page, L; Tucker, G S; Weiland, J; Wollack, E; Wright, E L
2003-01-01
We present the angular power spectrum derived from the first-year Wilkinson Microwave Anisotropy Probe (WMAP) sky maps. We study a variety of power spectrum estimation methods and data combinations and demonstrate that the results are robust. The data are modestly contaminated by diffuse Galactic foreground emission, but we show that a simple Galactic template model is sufficient to remove the signal. Point sources produce a modest contamination in the low frequency data. After masking ~700 known bright sources from the maps, we estimate residual sources contribute ~3500 uK^2 at 41 GHz, and ~130 uK^2 at 94 GHz, to the power spectrum l*(l+1)*C_l/(2*pi) at l=1000. Systematic errors are negligible compared to the (modest) level of foreground emission. Our best estimate of the power spectrum is derived from 28 cross-power spectra of statistically independent channels. The final spectrum is essentially independent of the noise properties of an individual radiometer. The resulting spectrum provides a definitive mea...
CENTER FOR PULSED POWER DRIVEN HIGH ENERGY DENSITY PLASMA STUDIES
Energy Technology Data Exchange (ETDEWEB)
Professor Bruce R. Kusse; Professor David A. Hammer
2007-04-18
This annual report summarizes the activities of the Cornell Center for Pulsed-Power-Driven High-Energy-Density Plasma Studies, for the 12-month period October 1, 2005-September 30, 2006. This period corresponds to the first year of the two-year extension (awarded in October, 2005) to the original 3-year NNSA/DOE Cooperative Agreement with Cornell, DE-FC03-02NA00057. As such, the period covered in this report also corresponds to the fourth year of the (now) 5-year term of the Cooperative Agreement. The participants, in addition to Cornell University, include Imperial College, London (IC), the University of Nevada, Reno (UNR), the University of Rochester (UR), the Weizmann Institute of Science (WSI), and the P.N. Lebedev Physical Institute (LPI), Moscow. A listing of all faculty, technical staff and students, both graduate and undergraduate, who participated in Center research activities during the year in question is given in Appendix A.
Electronic properties of solids excited with intermediate laser power densities
Sirotti, Fausto; Tempo Beamline Team
Intermediate laser power density up to about 100 GW/cm2 is below the surface damage threshold is currently used to induce modification in the physical properties on short time scales. The absorption of a short laser pulse induces non-equilibrium electronic distributions followed by lattice-mediated equilibrium taking place only in the picosecond range. The role of the hot electrons is particularly important in several domains as for example fast magnetization and demagnetization processes, laser induced phase transitions, charge density waves. Angular resolved photoelectron spectroscopy measuring directly energy and momentum of electrons is the most adapted tool to study the electronic excitations at short time scales during and after fast laser excitations. The main technical problem is the space charge created by the pumping laser pulse. I will present angular resolved multiphoton photoemission results obtained with 800 nm laser pulses showing how space charge electrons emitted during fast demagnetization processes can be measured. Unable enter Affiliation: CNRS-SOLEIL Synchrotron L'Orme des Merisiers , Saint Aubin 91192 Gif sur Yvette France.
Electromagnetic potentials basis for energy density and power flux
Puthoff, H. E.
2016-09-01
In rounding out the education of students in advanced courses in applied electromagnetics it is incumbent on us as mentors to raise issues that encourage appreciation of certain subtle aspects that are often overlooked during first exposure to the field. One of these has to do with the interplay between fields and potentials, with the latter often seen as just a convenient mathematical artifice useful in solving Maxwell’s equations. Nonetheless, to those practiced in application it is well understood that various alternatives in the use of fields and potentials are available within electromagnetic (EM) theory for the definitions of energy density, momentum transfer, EM stress-energy tensor, and so forth. Although the various options are all compatible with the basic equations of electrodynamics (e.g., Maxwell’s equations, Lorentz force law, gauge invariance), nonetheless certain alternative formulations lend themselves to being seen as preferable to others with regard to the transparency of their application to physical problems of interest. Here we argue for the transparency of an energy density/power flux option based on the EM potentials alone.
Białous, Małgorzata; Yunko, Vitalii; Bauch, Szymon; Ławniczak, Michał; Dietz, Barbara; Sirko, Leszek
2016-09-01
We present experimental studies of the power spectrum and other fluctuation properties in the spectra of microwave networks simulating chaotic quantum graphs with violated time reversal invariance. On the basis of our data sets, we demonstrate that the power spectrum in combination with other long-range and also short-range spectral fluctuations provides a powerful tool for the identification of the symmetries and the determination of the fraction of missing levels. Such a procedure is indispensable for the evaluation of the fluctuation properties in the spectra of real physical systems like, e.g., nuclei or molecules, where one has to deal with the problem of missing levels.
DEFF Research Database (Denmark)
Høgfeldt Hansen, Leif
2016-01-01
The publication functions as a proces description of the development and construction of an urban furniture SPECTRUM in the city of Gwangju, Republic of Korea. It is used as the cataloque for the exhibition of Spectrum.......The publication functions as a proces description of the development and construction of an urban furniture SPECTRUM in the city of Gwangju, Republic of Korea. It is used as the cataloque for the exhibition of Spectrum....
High Performance Power Spectrum Analysis Using a FPGA Based Reconfigurable Computing Platform
Abhyankar, Yogindra; Agarwal, Yogesh; Subrahmanya, C R; Prasad, Peeyush; 10.1109/RECONF.2006.307786
2011-01-01
Power-spectrum analysis is an important tool providing critical information about a signal. The range of applications includes communication-systems to DNA-sequencing. If there is interference present on a transmitted signal, it could be due to a natural cause or superimposed forcefully. In the latter case, its early detection and analysis becomes important. In such situations having a small observation window, a quick look at power-spectrum can reveal a great deal of information, including frequency and source of interference. In this paper, we present our design of a FPGA based reconfigurable platform for high performance power-spectrum analysis. This allows for the real-time data-acquisition and processing of samples of the incoming signal in a small time frame. The processing consists of computation of power, its average and peak, over a set of input values. This platform sustains simultaneous data streams on each of the four input channels.
Detection of a high frequency break in the X-ray power spectrum of Ark 564
Papadakis, I E; Negoro, H; Gliozzi, M
2001-01-01
We present a power spectrum analysis of the long ASCA observation of Ark 564 in June/July 2001. The observed power spectrum covers a frequency range of ~ 3.5 decades. We detect a high frequency break at ~ 0.002 Hz. The power spectrum has an rms of ~30% and a slope of ~ -1 and ~ -2 below and above the break frequency. When combined with the results from a long RXTE observation (Pounds et al. 2001), the observed power spectra of Ark 564 and Cyg X-1 (in the low/hard state) are almost identical, showing a similar shape and rms amplitude. However, the ratio of the high frequency breaks is very small (~ 10e{3-4}), implying that these characteristic frequencies are not indicative of the black hole mass. This result supports the idea of a small black hole mass/high accretion rate in Ark 564.
The CMB power spectrum out to l=1400 measured by the VSA
Grainge, K; Cleary, K; Davies, R D; Davis, R J; Dickinson, C; Genova-Santos, R; Gutíerrez, C M; Hafez, Y A; Hobson, M P; Jones, M E; Kneissl, R; Lancaster, K; Lasenby, A; Leahy, J P; Maisinger, K; Pooley, G G; Rebolo, R; Rubiño-Martín, J A; Molina, P S; Odman, C; Rusholme, B A; Saunders, R D E; Savage, R; Scott, P F; Slosar, A; Taylor, A C; Titterington, D; Waldram, E M; Watson, R A; Wilkinson, A; Grainge, Keith; Carreira, Pedro; Cleary, Kieran; Davies, Rod D.; Davis, Richard J.; Dickinson, Clive; Genova-Santos, Ricardo; Gutierrez, Carlos M.; Hafez, Yaser A.; Hobson, Michael P.; Jones, Michael E.; Kneissl, Rudiger; Lancaster, Katy; Lasenby, Anthony; Maisinger, Klaus; Pooley, Guy G.; Rebolo, Rafael; Rubino-Martin, Jose Alberto; Molina, Pedro Sosa; Odman, Carolina; Rusholme, Ben; Saunders, Richard D.E.; Savage, Richard; Scott, Paul F.; Slosar, Anze; Taylor, Angela C.; Titterington, David; Waldram, Elizabeth; Watson, Robert A.; Wilkinson, Althea
2003-01-01
We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.
Liu, Jia; Hill, J. Colin; Sherwin, Blake D.; Petri, Andrea; Böhm, Vanessa; Haiman, Zoltán
2016-11-01
Unprecedentedly precise cosmic microwave background (CMB) data are expected from ongoing and near-future CMB stage III and IV surveys, which will yield reconstructed CMB lensing maps with effective resolution approaching several arcminutes. The small-scale CMB lensing fluctuations receive non-negligible contributions from nonlinear structure in the late-time density field. These fluctuations are not fully characterized by traditional two-point statistics, such as the power spectrum. Here, we use N -body ray-tracing simulations of CMB lensing maps to examine two higher-order statistics: the lensing convergence one-point probability distribution function (PDF) and peak counts. We show that these statistics contain significant information not captured by the two-point function and provide specific forecasts for the ongoing stage III Advanced Atacama Cosmology Telescope (AdvACT) experiment. Considering only the temperature-based reconstruction estimator, we forecast 9 σ (PDF) and 6 σ (peaks) detections of these statistics with AdvACT. Our simulation pipeline fully accounts for the non-Gaussianity of the lensing reconstruction noise, which is significant and cannot be neglected. Combining the power spectrum, PDF, and peak counts for AdvACT will tighten cosmological constraints in the Ωm-σ8 plane by ≈30 %, compared to using the power spectrum alone.
Paul, Sourabh; Morales, Miguel F; Dwarkanath, K S; Shankar, N Udaya; Subrahmanyan, Ravi; Barry, N; Beardsley, A P; Bowman, Judd D; Briggs, F; Carroll, P; de Oliveira-Costa, A; Dillon, Joshua S; Ewall-Wice, A; Feng, L; Greenhill, L J; Gaensler, B M; Hazelton, B J; Hewitt, J N; Hurley-Walker, N; Jacobs, D J; Kim, Han-Seek; Kittiwisit, P; Lenc, E; Line, J; Loeb, A; McKinley, B; Mitchell, D A; Neben, A R; Offringa, A R; Pindor, B; Pober, J C; Procopio, P; Riding, J; Sullivan, I S; Tegmark, M; Thyagarajan, Nithyanandan; Tingay, S J; Trott, C M; Wayth, R B; Webster, R L; Wyithe, J S B; Cappallo, Roger; Johnston-Hollitt, M; Kaplan, D L; Lonsdale, C J; McWhirter, S R; Morgan, E; Oberoi, D; Ord, S M; Prabu, T; Srivani, K S; Williams, A; Williams, C L
2016-01-01
The Detection of redshifted 21 cm emission from the epoch of reionization (EoR) is a challenging task owing to strong foregrounds that dominate the signal. In this paper, we propose a general method, based on the delay spectrum approach, to extract HI power spectra that is applicable to tracking observations using an imaging radio interferometer (Delay Spectrum with Imaging Arrays (DSIA)). Our method is based on modelling the HI signal taking into account the impact of wide field effects such as the $w$-term which are then used as appropriate weights in cross-correlating the measured visibilities. Our method is applicable to any radio interferometer that tracks a phase center and could be utilized for arrays such as MWA, LOFAR, GMRT, PAPER and HERA. In the literature the delay spectrum approach has been implemented for near-redundant baselines using drift scan observations. In this paper we explore the scheme for non-redundant tracking arrays, and this is the first application of delay spectrum methodology to...
Adaptive discrete rate and power transmission for spectrum sharing systems
Abdallah, Mohamed M.
2012-04-01
In this paper we develop a framework for optimizing the performance of the secondary link in terms of the average spectral efficiency assuming quantized channel state information (CSI) of the secondary and the secondary-to-primary interference channels available at the secondary transmitter. We consider the problem under the constraints of maximum average interference power levels at the primary receiver. We develop a sub-optimal computationally efficient iterative algorithm for finding the optimal CSI quantizers as well as the discrete power and rate employed at the cognitive transmitter for each quantized CSI level so as to maximize the average spectral efficiency. We show via analysis and simulations that the proposed algorithm converges for Rayleigh fading channels. Our numerical results give the number of bits required to sufficiently represent the CSI to achieve almost the maximum average spectral efficiency attained using full knowledge of the CSI. © 2012 IEEE.
Loeb, Abraham; Wyithe, J Stuart B
2008-04-25
Measurements of the 21 cm line emission by residual cosmic hydrogen after reionization can be used to trace the power spectrum of density perturbations through a significant fraction of the observable volume of the Universe. We show that a dedicated 21 cm observatory could probe a number of independent modes that is 2 orders of magnitude larger than currently available, and enable a cosmic-variance limited detection of the signature of a neutrino mass approximately 0.05 eV. The evolution of the linear growth factor with redshift could also constrain exotic theories of gravity or dark energy to an unprecedented precision.
Contamination of the Epoch of Reionization power spectrum in the presence of foregrounds
Sims, Peter H.; Lentati, Lindley; Alexander, Paul; Carilli, Chris L.
2016-01-01
We construct foreground simulations comprising spatially correlated extragalactic and diffuse Galactic emission components and calculate the `intrinsic' (instrument-free) two-dimensional spatial power spectrum and the cylindrically and spherically averaged three-dimensional k-space power spectra of the Epoch of Reionization (EoR) and our foreground simulations using a Bayesian power spectral estimation framework. This leads us to identify a model dependent region of optimal signal estimation ...
Predictions for the 21cm-galaxy cross-power spectrum observable with LOFAR and Subaru
Vrbanec, Dijana; Jelić, Vibor; Jensen, Hannes; Zaroubi, Saleem; Fernandez, Elizabeth R; Ghosh, Abhik; Iliev, Ilian T; Kakiichi, Koki; Koopmans, Léon V E; Mellema, Garrelt
2016-01-01
The 21cm-galaxy cross-power spectrum is expected to be one of the promising probes of the Epoch of Reionization (EoR), as it could offer information about the progress of reionization and the typical scale of ionized regions at different redshifts. With upcoming observations of 21cm emission from the EoR with the Low Frequency Array (LOFAR), and of high redshift Lyalpha emitters (LAEs) with Subaru's Hyper Suprime Cam (HSC), we investigate the observability of such cross-power spectrum with these two instruments, which are both planning to observe the ELAIS-N1 field at z=6.6. In this paper we use N-body + radiative transfer (both for continuum and Lyalpha photons) simulations at redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21cm-galaxy cross-power spectrum, as well as to predict the 2D 21cm-galaxy cross-power spectrum expected to be observed by LOFAR and HSC. Once noise and projection effects are accounted for, our predictions of the 21cm-galaxy cross-power spectrum show clear anti-correlation on s...
Simulations of Baryon Acoustic Oscillations II: Covariance matrix of the matter power spectrum
Takahashi, Ryuichi; Takada, Masahiro; Matsubara, Takahiko; Sugiyama, Naoshi; Kayo, Issha; Nishizawa, Atsushi J; Nishimichi, Takahiro; Saito, Shun; Taruya, Atsushi
2009-01-01
We use 5000 cosmological N-body simulations of 1(Gpc/h)^3 box for the concordance LCDM model in order to study the sampling variances of nonlinear matter power spectrum. We show that the non-Gaussian errors can be important even on large length scales relevant for baryon acoustic oscillations (BAO). Our findings are (1) the non-Gaussian errors degrade the cumulative signal-to-noise ratios (S/N) for the power spectrum amplitude by up to a factor of 2 and 4 for redshifts z=1 and 0, respectively. (2) There is little information on the power spectrum amplitudes in the quasi-nonlinear regime, confirming the previous results. (3) The distribution of power spectrum estimators at BAO scales, among the realizations, is well approximated by a Gaussian distribution with variance that is given by the diagonal covariance component. (4) For the redshift-space power spectrum, the degradation in S/N by non-Gaussian errors is mitigated due to nonlinear redshift distortions. (5) For an actual galaxy survey, the additional shot...
Study on load forecasting to data centers of high power density based on power usage effectiveness
Zhou, C. C.; Zhang, F.; Yuan, Z.; Zhou, L. M.; Wang, F. M.; Li, W.; Yang, J. H.
2016-08-01
There is usually considerable energy consumption in data centers. Load forecasting to data centers is in favor of formulating regional load density indexes and of great benefit to getting regional spatial load forecasting more accurately. The building structure and the other influential factors, i.e. equipment, geographic and climatic conditions, are considered for the data centers, and a method to forecast the load of the data centers based on power usage effectiveness is proposed. The cooling capacity of a data center and the index of the power usage effectiveness are used to forecast the power load of the data center in the method. The cooling capacity is obtained by calculating the heat load of the data center. The index is estimated using the group decision-making method of mixed language information. An example is given to prove the applicability and accuracy of this method.
Kashima, Susumu; Nishihara, Minoru; Takemoto, Yoshihiro; Osawa, Toshihiko
1990-09-01
The laser scattering characteristics from tissue microvasculature have been made clear by means of theoretical and experimental approaches. Our results show that the integrated intensity of the power spectrum correlates linearly with the volume of red blood cells in a given tissue provided the average collision number (\\bar{m}) between photons and moving red blood cells is less than unity. Also, the integrated intensity of the power spectrum is proportional to tissue blood volume if the density of red blood cells in blood (hematocrit) is constant.
The spectrum of large powers of the Laplacian in bounded domains
Energy Technology Data Exchange (ETDEWEB)
Katzav, E; Adda-Bedia, M [Laboratoire de Physique Statistique de l' Ecole Normale Superieure, CNRS UMR 8550, 24 rue Lhomond, 75231 Paris Cedex 05 (France)
2008-01-18
We present exact results for the spectrum of the Nth power of the Laplacian in a bounded domain. We begin with the one-dimensional case and show that the whole spectrum can be obtained in the limit of large N. We also show that it is a useful numerical approach valid for any N. Finally, we discuss implications of this work and present its possible extensions for non-integer N and for 3D Laplacian problems. (fast track communication)
Operational modal analysis using SVD of power spectral density transmissibility matrices
Araújo, Iván Gómez; Laier, Jose Elias
2014-05-01
This paper proposes the singular value decomposition of power spectrum density transmissibility matrices with different references, (PSDTM-SVD), as an identification method of natural frequencies and mode shapes of a dynamic system subjected to excitations under operational conditions. At the system poles, the rows of the proposed transmissibility matrix converge to the same ratio of amplitudes of vibration modes. As a result, the matrices are linearly dependent on the columns, and their singular values converge to zero. Singular values are used to determine the natural frequencies, and the first left singular vectors are used to estimate mode shapes. A numerical example of the finite element model of a beam subjected to colored noise excitation is analyzed to illustrate the accuracy of the proposed method. Results of the PSDTM-SVD method in the numerical example are compared with obtained using frequency domain decomposition (FDD) and power spectrum density transmissibility (PSDT). It is demonstrated that the proposed method does not depend on the excitation characteristics contrary to the FDD method that assumes white noise excitation, and further reduces the risk to identify extra non-physical poles in comparison to the PSDT method. Furthermore, a case study is performed using data from an operational vibration test of a bridge with a simply supported beam system. The real application of a full-sized bridge has shown that the proposed PSDTM-SVD method is able to identify the operational modal parameter. Operational modal parameters identified by the PSDTM-SVD in the real application agree well those identified by the FDD and PSDT methods.
Violation of statistical isotropy and homogeneity in the 21-cm power spectrum
Shiraishi, Maresuke; Kamionkowski, Marc; Raccanelli, Alvise
2016-01-01
Most inflationary models predict primordial perturbations to be statistically isotropic and homogeneous. Cosmic-Microwave-Background (CMB) observations, however, indicate a possible departure from statistical isotropy in the form of a dipolar power modulation at large angular scales. Alternative models of inflation, beyond the simplest single-field slow-roll models, can generate a small power asymmetry, consistent with these observations. Observations of clustering of quasars show, however, agreement with statistical isotropy at much smaller angular scales. Here we propose to use off-diagonal components of the angular power spectrum of the 21-cm fluctuations during the dark ages to test this power asymmetry. We forecast results for the planned SKA radio array, a future radio array, and the cosmic-variance-limited case as a theoretical proof of principle. Our results show that the 21-cm-line power spectrum will enable access to information at very small scales and at different redshift slices, thus improving u...
Mass Power Spectrum in a Universe Dominated by the Chaplygin Gas
Fabris, J C
2002-01-01
The mass power spectrum for a Universe dominated by the Chaplygin gas is evaluated numerically from scales of the order of the Hubble horizon to 100 Mpc. The results are compared with a pure baryonic Universe and a cosmological constant model. In all three cases, the spectrum increases with k, the wavenumber of the perturbations. The slope of the spectrum is higher for the baryonic model and smaller for the cosmological constant model, the Chaplygin gas interpolating these two models. The results are analyzed in terms of the sound velocity of the Chaplygin gas and the moment the Universe begins to accelerate.
Planck scale effects and the suppression of power on the large scales in the primordial spectrum
Shankaranarayanan, S
2005-01-01
The enormous red-shifting of the modes during the inflationary epoch suggests that physics at the very high energy scales may modify the primordial perturbation spectrum. Therefore, the measurements of the anisotropies in the Cosmic Microwave Background (CMB) could provide us with clues to understanding physics beyond the Planck scale. In this proceeding, we study the Planck scale effects on the primordial spectrum in the power-law inflation using a model which preserves local Lorentz invariance. While our model reproduces the standard spectrum on small scales, it naturally predicts a suppression of power on the large scales -- a feature that seems to be necessary to explain deficit of power in the lower multipoles of the CMB.
Constraining High Redshift X-ray Sources with Next Generation 21 cm Power Spectrum Measurements
Ewall-Wice, Aaron; Mesinger, Andrei; Dillon, Joshua S; Liu, Adrian; Pober, Jonathan
2015-01-01
We use the Fisher matrix formalism and semi-numerical simulations to derive quantitative predictions of the constraints that power spectrum measurements on next-generation interferometers, such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA), will place on the characteristics of the X-ray sources that heated the high redshift intergalactic medium. Incorporating observations between $z=5$ and $z=25$, we find that the proposed 331 element HERA and SKA phase 1 will be capable of placing $\\lesssim 10\\%$ constraints on the spectral properties of these first X-ray sources, even if one is unable to perform measurements within the foreground contaminated "wedge" or the FM band. When accounting for the enhancement in power spectrum amplitude from spin temperature fluctuations, we find that the observable signatures of reionization extend well beyond the peak in the power spectrum usually associated with it. We also find that lower redshift degeneracies between the signatures of ...
Contamination of the Epoch of Reionization power spectrum in the presence of foregrounds
Sims, Peter H.; Lentati, Lindley; Alexander, Paul; Carilli, Chris L.
2016-11-01
We construct foreground simulations comprising spatially correlated extragalactic and diffuse Galactic emission components and calculate the `intrinsic' (instrument-free) two-dimensional spatial power spectrum and the cylindrically and spherically averaged three-dimensional k-space power spectra of the Epoch of Reionization (EoR) and our foreground simulations using a Bayesian power spectral estimation framework. This leads us to identify a model-dependent region of optimal signal estimation for our foreground and EoR models, within which the spatial power in the EoR signal relative to the foregrounds is maximized. We identify a target field-dependent region, in k-space, of intrinsic foreground power spectral contamination at low k⊥ and k∥ and a transition to a relatively foreground-free intrinsic EoR window in the complement to this region. The contaminated region of k-space demonstrates that simultaneous estimation of the EoR and foregrounds is important for obtaining statistically robust estimates of the EoR power spectrum; biased results will be obtained from methodologies that ignore their covariance. Using simulated observations with frequency-dependent uv-coverage and primary beam, with the former derived for the Hydrogen Epoch of Reionization Array in 37-antenna and 331-antenna configuration, we recover instrumental power spectra consistent with their intrinsic counterparts. We discuss the implications of these results for optimal strategies for unbiased estimation of the EoR power spectrum.
Power spectrum nulls due to non-standard inflationary evolution
Goswami, Gaurav
2010-01-01
The simplest models of inflation based on slow roll produce nearly scale invariant primordial power spectra (PPS). But there are also numerous models that predict radically broken scale invariant PPS. In particular, markedly cuspy dips in the PPS correspond to nulls where the perturbation amplitude, hence PPS, goes through a zero at a specific wavenumber. Near this wavenumber, the true quantum nature of the generation mechanism of the primordial fluctuations may be revealed. Naively these features may appear to arise from fine tuned initial conditions. However, we show that this behavior arises under fairly generic set of conditions involving super-Hubble scale evolution of perturbation modes during inflation. We illustrate this with the well-studied examples of punctuated inflation and the Starobinsky-break model.
A High Power Density Power System Electronics for NASA's Lunar Reconnaissance Orbiter
Hernandez-Pellerano, A.; Stone, R.; Travis, J.; Kercheval, B.; Alkire, G.; Ter-Minassian, V.
2009-01-01
A high power density, modular and state-of-the-art Power System Electronics (PSE) has been developed for the Lunar Reconnaissance Orbiter (LRO) mission. This paper addresses the hardware architecture and performance, the power handling capabilities, and the fabrication technology. The PSE was developed by NASA s Goddard Space Flight Center (GSFC) and is the central location for power handling and distribution of the LRO spacecraft. The PSE packaging design manages and distributes 2200W of solar array input power in a volume less than a cubic foot. The PSE architecture incorporates reliable standard internal and external communication buses, solid state circuit breakers and LiIon battery charge management. Although a single string design, the PSE achieves high reliability by elegantly implementing functional redundancy and internal fault detection and correction. The PSE has been environmentally tested and delivered to the LRO spacecraft for the flight Integration and Test. This modular design is scheduled to flight in early 2009 on board the LRO and Lunar Crater Observation and Sensing Satellite (LCROSS) spacecrafts and is the baseline architecture for future NASA missions such as Global Precipitation Measurement (GPM) and Magnetospheric MultiScale (MMS).
Statistical connection of peak counts to power spectrum and moments in weak lensing field
Shirasaki, Masato
2016-01-01
The number density of local maxima of weak lensing field, referred to as weak-lensing peak counts, can be used as a cosmological probe. However, its relevant cosmological information is still unclear. We study the relationship between the peak counts and other statistics in weak lensing field by using 1000 ray-tracing simulations. We construct a local transformation of lensing field $\\cal K$ to a new Gaussian field $y$, named local-Gaussianized transformation. We calibrate the transformation with numerical simulations so that the one-point distribution and the power spectrum of $\\cal K$ can be reproduced from a single Gaussian field $y$ and monotonic relation between $y$ and $\\cal K$. Therefore, the correct information of two-point clustering and any order of moments in weak lensing field should be preserved under local-Gaussianized transformation. We then examine if local-Gaussianized transformation can predict weak-lensing peak counts in simulations. The local-Gaussianized transformation is insufficient to ...
Convolution power spectrum analysis for FMRI data based on prior image signal.
Zhang, Jiang; Chen, Huafu; Fang, Fang; Liao, Wei
2010-02-01
Functional MRI (fMRI) data-processing methods based on changes in the time domain involve, among other things, correlation analysis and use of the general linear model with statistical parametric mapping (SPM). Unlike conventional fMRI data analysis methods, which aim to model the blood-oxygen-level-dependent (BOLD) response of voxels as a function of time, the theory of power spectrum (PS) analysis focuses completely on understanding the dynamic energy change of interacting systems. We propose a new convolution PS (CPS) analysis of fMRI data, based on the theory of matched filtering, to detect brain functional activation for fMRI data. First, convolution signals are computed between the measured fMRI signals and the image signal of prior experimental pattern to suppress noise in the fMRI data. Then, the PS density analysis of the convolution signal is specified as the quantitative analysis energy index of BOLD signal change. The data from simulation studies and in vivo fMRI studies, including block-design experiments, reveal that the CPS method enables a more effective detection of some aspects of brain functional activation, as compared with the canonical PS SPM and the support vector machine methods. Our results demonstrate that the CPS method is useful as a complementary analysis in revealing brain functional information regarding the complex nature of fMRI time series.
High power densities from high-temperature material interactions
Energy Technology Data Exchange (ETDEWEB)
Morris, J.F.
1981-01-01
Thermionic energy conversion (TEC) and metallic-fluid heat pipes (MFHPs) offer important and unique advantages in terrestrial and space energy processing. And they are well suited to serve together synergistically. TEC and MFHPs operate through working-fluid vaporization, condensation cycles that accept great thermal power densities at high temperatures. TEC and MFHPs have apparently simple, isolated performance mechanisms that are somewhat similar. And they also have obviously difficult, complected material problems that again are somewhat similar. Intensive investigation reveals that aspects of their operating cycles and material problems tend to merge: high-temperature material effects determine the level and lifetime of performance. Simplified equations verify the preceding statement for TEC and MFHPs. Material properties and interactions exert primary influences on operational effectiveness. And thermophysicochemical stabilities dictate operating temperatures which regulate the thermoemissive currents of TEC and the vaporization flow rates of MFHPs. Major high-temperature material problems of TEC and MFHPs have been solved. These solutions lead to productive, cost-effective applications of current TEC and MFHPs - and point to significant improvements with anticipated technological gains.
Scaling-law for the energy dependence of anatomic power spectrum in dedicated breast CT
Energy Technology Data Exchange (ETDEWEB)
Vedantham, Srinivasan; Shi, Linxi; Glick, Stephen J.; Karellas, Andrew [Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655 (United States)
2013-01-15
Purpose: To determine the x-ray photon energy dependence of the anatomic power spectrum of the breast when imaged with dedicated breast computed tomography (CT). Methods: A theoretical framework for scaling the empirically determined anatomic power spectrum at one x-ray photon energy to that at any given x-ray photon energy when imaged with dedicated breast CT was developed. Theory predicted that when the anatomic power spectrum is fitted with a power curve of the form k f{sup -{beta}}, where k and {beta} are fit coefficients and f is spatial frequency, the exponent {beta} would be independent of x-ray photon energy (E), and the amplitude k scales with the square of the difference in energy-dependent linear attenuation coefficients of fibroglandular and adipose tissues. Twenty mastectomy specimens based numerical phantoms that were previously imaged with a benchtop flat-panel cone-beam CT system were converted to 3D distribution of glandular weight fraction (f{sub g}) and were used to verify the theoretical findings. The 3D power spectrum was computed in terms of f{sub g} and after converting to linear attenuation coefficients at monoenergetic x-ray photon energies of 20-80 keV in 5 keV intervals. The 1D power spectra along the axes were extracted and fitted with a power curve of the form k f{sup -{beta}}. The energy dependence of k and {beta} were analyzed. Results: For the 20 mastectomy specimen based numerical phantoms used in the study, the exponent {beta} was found to be in the range of 2.34-2.42, depending on the axis of measurement. Numerical simulations agreed with the theoretical predictions that for a power-law anatomic spectrum of the form k f{sup -{beta}}, {beta} was independent of E and k(E) =k{sub 1}[{mu}{sub g}(E) -{mu}{sub a}(E)]{sup 2}, where k{sub 1} is a constant, and {mu}{sub g}(E) and {mu}{sub a}(E) represent the energy-dependent linear attenuation coefficients of fibroglandular and adipose tissues, respectively. Conclusions: Numerical
Directory of Open Access Journals (Sweden)
DURNEA, T. N.
2009-02-01
Full Text Available UWB-PPM systems were noted to have a power spectral density (p.s.d. consisting of a continuous portion and a line spectrum, which is composed of energy components placed at discrete frequencies. These components are the major source of interference to narrowband systems operating in the same frequency interval and deny harmless coexistence of UWB-PPM and narrowband systems. A new code denoted as Totally Flipped Code (TFC is applied to them in order to eliminate these discrete spectral components. The coded signal transports the information inside pulse position and will have the amplitude coded to generate a continuous p.s.d. We have designed the code and calculated the power spectral density of the coded signals. The power spectrum has no discrete components and its envelope is largely flat inside the bandwidth with a maximum at its center and a null at D.C. These characteristics make this code suited for implementation in the UWB systems based on PPM-type modulation as it assures a continuous spectrum and keeps PPM modulation performances.
A neutrino model fit to the CMB power spectrum
Shanks, T; Schewtschenko, J A; Whitbourn, J R
2014-01-01
The current standard cosmological model, LCDM, provides an excellent fit to the WMAP and Planck CMB data. However, the model has well known problems. For example, the cosmological constant is fine tuned to 1 part in 10^100 and the cold dark matter (CDM) particle is not yet detected in the laboratory. Here we seek an alternative model to LCDM which makes minimal assumptions about new physics. This is based on previous work by Shanks who investigated a model which assumed neither exotic particles nor a cosmological constant but instead postulated a low Hubble constant (H_0) to help allow a baryon density which was compatible with an inflationary model with zero spatial curvature. However, the recent Planck results make it more difficult to reconcile such a model with the cosmic microwave background (CMB) temperature fluctuations. Here we relax the previous assumptions to assess the effects of assuming standard model neutrinos of moderate mass (~5eV) but with no CDM and no cosmological constant. If we assume a l...
Primordial non-Gaussianity from the 21 cm power spectrum during the epoch of reionization.
Joudaki, Shahab; Doré, Olivier; Ferramacho, Luis; Kaplinghat, Manoj; Santos, Mario G
2011-09-23
Primordial non-Gaussianity is a crucial test of inflationary cosmology. We consider the impact of non-Gaussianity on the ionization power spectrum from 21 cm emission at the epoch of reionization. We focus on the power spectrum on large scales at redshifts of 7 to 8 and explore the expected constraint on the local non-Gaussianity parameter f(NL) for current and next-generation 21 cm experiments. We show that experiments such as SKA and MWA could measure f(NL) values of order 10. This can be improved by an order of magnitude with a fast-Fourier transform telescope like Omniscope.
Primordial Non-Gaussianity from the 21 cm Power Spectrum during the Epoch of Reionization
Joudaki, Shahab; Dore, Olivier; Ferramacho, Luis; Kaplinghat, Manoj; Santos, Mario G.
2011-01-01
Primordial non-Gaussianity is a crucial test of inflationary cosmology. We consider the impact of non-Gaussianity on the ionization power spectrum from 21 cm emission during the epoch of reionization. We focus on the power spectrum on large scales at redshifts of 7 to 8 and explore the expected constraint on the local non-Gaussianity parameter f_NL for current and next-generation 21 cm experiments. We show that experiments such as SKA and MWA could measure f_NL values of order 10. This can be...
A new method of measuring the cluster peculiar velocity power spectrum
Zhang, Pengjie; Juszkiewicz, Roman; Stebbins, Albert
2008-01-01
We propose to use spatial correlations of the kinetic Sunyaev-Zeldovich (KSZ) flux as an estimator of the peculiar velocity power spectrum. In contrast with conventional techniques, our new method does not require measurements of the thermal SZ signal or the X-ray temperature. Moreover, this method has the special advantage that the expected systematic errors are always sub-dominant to statistical errors on all scales and redshifts of interest. We show that future large sky coverage KSZ surveys may allow a peculiar velocity power spectrum estimates of an accuracy reaching ~10%.
Model independent signatures of new physics in the inflationary power spectrum.
Jackson, Mark G; Schalm, Koenraad
2012-03-16
We compute the universal generic corrections to the inflationary power spectrum due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the "in-in" formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. We find that the power spectrum is universally modified at order H/M, where H is the scale of inflation. This is qualitatively different from the universal corrections in time-independent backgrounds, and it suggests that such effects may be present in upcoming cosmological observations.
Modelling the autocovariance of the power spectrum of a solar-type oscillator
DEFF Research Database (Denmark)
Campante , T.L.; Karoff, Christoffer
2010-01-01
originates from a radial or a dipolar oscillation mode. In order to overcome this problem, we present a procedure for modelling and fitting the autocovariance of the power spectrum which can be used to obtain global seismic parameters of solar-type stars, doing so in an automated fashion without the need...... to make subjective choices. From the set of retrievable global seismic parameters we emphasize the mean small frequency separation and, depending on the intrinsic characteristics of the power spectrum, the mean rotational frequency splitting. Since this procedure is automated, it can serve as a useful...
Nasir, Fahad; Bolton, James S.; Becker, George D.
2016-12-01
We use cosmological hydrodynamical simulations to assess the feasibility of constraining the thermal history of the intergalactic medium during reionization with the Lyα forest at z ≃ 5. The integrated thermal history has a measurable impact on the transmitted flux power spectrum that can be isolated from Doppler broadening at this redshift. We parametrize this using the cumulative energy per proton, u0, deposited into a gas parcel at the mean background density, a quantity that is tightly linked with the gas density power spectrum in the simulations. We construct mock observations of the line-of-sight Lyα forest power spectrum and use a Markov Chain Monte Carlo approach to recover u0 at redshifts 5 ≲ z ≲ 12. A statistical uncertainty of ˜20 per cent is expected (at 68 per cent confidence) at z ≃ 5 using high-resolution spectra with a total redshift path length of Δz = 4 and a typical signal-to-noise ratio of 15 per pixel. Estimates for the expected systematic uncertainties are comparable, such that existing data should enable a measurement of u0 to within ˜30 per cent. This translates to distinguishing between reionization scenarios with similar instantaneous temperatures at z ≃ 5, but with an energy deposited per proton that differs by 2-3 eV over the redshift interval 5 ≲ z ≲ 12. For an initial temperature of T ˜ 104 K following reionization, this corresponds to the difference between early (zre = 12) and late (zre = 7) reionization in our models.
Xu, Meng-long; Yang, Chang-bao; Liu, Wan-song; Wu, Yan-gang; Zhang, Chen-xi
2015-08-01
It chooses 15 kinds of rock from the three major rock categories as the rock samples (the number of rock samples is 208) and obtains the density, susceptibility and reflection spectrum at the wave band of 350~2500 nm. It calculates the correlative coefficients with the aim of studying the characteristic relationship between the property (including the density and the susceptibility) of the rock and the reflectivity. It concludes the wave band of the reflection spectrum which owes the prospect to discuss the density and susceptibility of the rock qualitatively or quantitatively, meanwhile, it sums up the characteristic of the curves of the correlative coefficients. In this paper, the discussion and analysis based on the results show that the study on the character relationship between the property of rock (density and susceptibility) and the reflection spectrum is meaningful and workable.
Energy Technology Data Exchange (ETDEWEB)
Das, Sudeep [Argonne National Laboratory, 9700 S. Cass Ave., Lemont, IL 60439 (United States); Louis, Thibaut; Calabrese, Erminia; Dunkley, Joanna [Sub-department of Astrophysics, University of Oxford, Keble Road, Oxford, OX1 3RH (United Kingdom); Nolta, Michael R.; Bond, J Richard; Hajian, Amir; Hincks, Adam D. [Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON, M5S 3H8 Canada (Canada); Addison, Graeme E.; Halpern, Mark [Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, V6T 1Z4 Canada (Canada); Battistelli, Elia S. [Department of Physics, University of Rome ' ' La Sapienza' ' , Piazzale Aldo Moro 5, I-00185 Rome (Italy); Crichton, Devin; Gralla, Megan [Dept. of Physics and Astronomy, The Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218-2686 (United States); Devlin, Mark J.; Dicker, Simon [Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA, 19104 (United States); Dünner, Rolando [Departamento de Astronomía y Astrofísica, Facultad de Física, Pontificía Universidad Católica, Casilla 306, Santiago 22 (Chile); Fowler, Joseph W. [NIST Quantum Devices Group, 325 Broadway Mailcode 817.03, Boulder, CO, 80305 (United States); Hasselfield, Matthew; Hlozek, Renée [Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ 08544 (United States); Hilton, Matt, E-mail: sudeepphys@gmail.com [Centre for Astronomy and Particle Theory, School of Physics and Astronomy, University of Nottingham, NG7 2RD (United Kingdom); and others
2014-04-01
We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. We detect and correct for contamination due to the Galactic cirrus in our equatorial maps. We present the results of a number of tests for possible systematic error and conclude that any effects are not significant compared to the statistical errors we quote. Where they overlap, we cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they are consistent. The measurements of higher-order peaks in the CMB power spectrum provide an additional test of the ΛCDM cosmological model, and help constrain extensions beyond the standard model. The small angular scale power spectrum also provides constraining power on the Sunyaev-Zel'dovich effects and extragalactic foregrounds. We also present a measurement of the CMB gravitational lensing convergence power spectrum at 4.6σ detection significance.
Kayo, Issha
2013-01-01
We re-examine a genuine power of weak lensing bispectrum tomography for constraining cosmological parameters, when combined with the power spectrum tomography, based on the Fisher information matrix formalism. To account for the full information at two- and three-point levels, we include all the power spectrum and bispectrum information built from all-available combinations of tomographic redshift bins, multipole bins and different triangle configurations over a range of angular scales (up to lmax=2000 as our fiducial choice). For the parameter forecast, we use the halo model approach in Kayo, Takada & Jain (2013) to model the non-Gaussian error covariances as well as the cross-covariance between the power spectrum and the bispectrum, including the halo sample variance or the nonlinear version of beat-coupling. We find that adding the bispectrum information leads to about 60% improvement in the dark energy figure-of-merit compared to the lensing power spectrum tomography alone, for three redshift-bin tomo...
Das, Sudeep; Louis, Thibaut; Nolta, Michael R.; Addison, Graeme E.; Battisetti, Elia S.; Bond, J. Richard; Calabrese, Erminia; Crichton, Devin; Devlin, Mark J.; Dicker, Simon;
2014-01-01
We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. We detect and correct for contamination due to the Galactic cirrus in our equatorial maps. We present the results of a number of tests for possible systematic error and conclude that any effects are not significant compared to the statistical errors we quote. Where they overlap, we cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they are consistent. The measurements of higher-order peaks in the CMB power spectrum provide an additional test of the ?CDM cosmological model, and help constrain extensions beyond the standard model. The small angular scale power spectrum also provides constraining power on the Sunyaev-Zel'dovich effects and extragalactic foregrounds. We also present a measurement of the CMB gravitational lensing convergence power spectrum at 4.6s detection significance.
Baryon impact on weak lensing peaks and power spectrum: low-bias statistics and self-calibration in future surveys
Yang, Xiuyuan; Huffenberger, Kevin; Haiman, Zoltán; May, Morgan
2012-01-01
Peaks in two-dimensional weak lensing (WL) maps contain significant cosmological information, complementary to the WL power spectrum. This has recently been demonstrated using N-body simulations which neglect baryonic effects. Here we employ ray-tracing N-body simulations in which we manually steepen the density profile of each dark matter halo, mimicking the cooling and concentration of baryons into dark matter potential wells. We find, in agreement with previous works, that this causes a significant increase in the amplitude of the WL power spectrum on small scales (spherical harmonic index l>1,000). We then study the impact of the halo concentration increase on the peak counts, and find the following. (i) Low peaks (with convergence 0.02 0.5 R_vir); as a result, they are insensitive to the central halo density profiles. These peaks contain most of the cosmological information, and thus provide an unusually sensitive and unbiased probe. (ii) The number of high peaks (with convergence kappa_peak > 0.08) is ...
Hou, Dong; Wang, Jingwei; Gao, Lijun; Liang, Xuejie; Li, Xiaoning; Liu, Xingsheng
2016-03-01
The high power diode lasers have been widely used in many fields. In this work, a sophisticated high power and high performance horizontal array of diode laser stacks have been developed and fabricated with high duty cycle using hard solder bonding technology. CTE-matched submount and Gold Tin (AuSn) hard solder are used for bonding the diode laser bar to achieve the performances of anti-thermal fatigue, higher reliability and longer lifetime. This array consists of 30 bars with the expected optical output peak power of 6000W. By means of numerical simulation and analytical results, the diode laser bars are aligned on suitable positions along the water cooled cooler in order to achieve the uniform wavelength with narrow spectrum and accurate central wavelength. The performance of the horizontal array, such as output power, spectrum, thermal resistance, life time, etc., is characterized and analyzed.
Power Control for Maximum Throughput in Spectrum Underlay Cognitive Radio Networks
Tadrous, John; Nafie, Mohammed; El-Keyi, Amr
2010-01-01
We investigate power allocation for users in a spectrum underlay cognitive network. Our objective is to find a power control scheme that allocates transmit power for both primary and secondary users so that the overall network throughput is maximized while maintaining the quality of service (QoS) of the primary users greater than a certain minimum limit. Since an optimum solution to our problem is computationally intractable, as the optimization problem is non-convex, we propose an iterative algorithm based on sequential geometric programming, that is proved to converge to at least a local optimum solution. We use the proposed algorithm to show how a spectrum underlay network would achieve higher throughput with secondary users operation than with primary users operating alone. Also, we show via simulations that the loss in primary throughput due to the admission of the secondary users is accompanied by a reduction in the total primary transmit power.
What can be learned from the lensed cosmic microwave background B-mode polarization power spectrum?
Smith, S; Rocha, G; Smith, Sarah; Challinor, Anthony; Rocha, Graca
2006-01-01
The effect of weak gravitational lensing on the cosmic microwave background (CMB) temperature anisotropies and polarization will provide access to cosmological information that cannot be obtained from the primary anisotropies alone. We compare the information content of the lensed B-mode polarization power spectrum, properly accounting for the non-Gaussian correlations between the power on different scales, with that of the unlensed CMB fields and the lensing potential. The latter represent the products of an (idealised) optimal analysis that exploits the lens-induced non-Gaussianity to reconstruct the fields. Compressing the non-Gaussian lensed CMB into power spectra is wasteful and leaves a tight degeneracy between the equation of state of dark energy and neutrino mass that is much stronger than in the more optimal analysis. Despite this, a power spectrum analysis will be a useful first step in analysing future B-mode polarization data. For this reason, we also consider how to extract accurate parameter con...
Fault Feature Extraction of Rolling Bearing Based on an Improved Cyclical Spectrum Density Method
Institute of Scientific and Technical Information of China (English)
LI Min; YANG Jianhong; WANG Xiaojing
2015-01-01
The traditional cyclical spectrum density(CSD) method is widely used to analyze the fault signals of rolling bearing. All modulation frequencies are demodulated in the cyclic frequency spectrum. Consequently, recognizing bearing fault type is difficult. Therefore, a new CSD method based on kurtosis(CSDK) is proposed. The kurtosis value of each cyclic frequency is used to measure the modulation capability of cyclic frequency. When the kurtosis value is large, the modulation capability is strong. Thus, the kurtosis value is regarded as the weight coefficient to accumulate all cyclic frequencies to extract fault features. Compared with the traditional method, CSDK can reduce the interference of harmonic frequency in fault frequency, which makes fault characteristics distinct from background noise. To validate the effectiveness of the method,experiments are performed on the simulation signal, the fault signal of the bearing outer race in the test bed, and the signal gathered from the bearing of the blast furnace belt cylinder. Experimental results show that the CSDK is better than the resonance demodulation method and the CSD in extracting fault features and recognizing degradation trends. The proposed method provides a new solution to fault diagnosis in bearings.
Saito, Shun; Vlah, Zvonimir; Seljak, Uroš; Okumura, Teppei; McDonald, Patrick
2014-01-01
Understanding the relation between underlying matter distribution and biased tracers such as galaxy or dark matter halo is essential to extract cosmological information from ongoing or future galaxy redshift surveys. At sufficiently large scales such as the BAO scale, a standard approach for the bias problem on the basis of the perturbation theory (PT) is to assume the `local bias' model in which the density field of biased tracers is deterministically expanded in terms of matter density field at the same position. The higher-order bias parameters are then determined by combining the power spectrum with higher-order statistics such as the bispectrum. As is pointed out by recent studies, however, nonlinear gravitational evolution naturally induces nonlocal bias terms even if initially starting only with purely local bias. As a matter of fact, previous works showed that the second-order nonlocal bias term, which corresponds to the gravitational tidal field, is important to explain the characteristic scale-depen...
Ruling out the power-law form of the scalar primordial spectrum
Energy Technology Data Exchange (ETDEWEB)
Hazra, Dhiraj Kumar; Shafieloo, Arman [Asia Pacific Center for Theoretical Physics, Pohang, Gyeongbuk 790-784 (Korea, Republic of); Smoot, George F. [Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Starobinsky, Alexei A., E-mail: dhiraj@apctp.org, E-mail: arman@apctp.org, E-mail: gfsmoot@lbl.gov, E-mail: alstar@landau.ac.ru [Landau Institute for Theoretical Physics RAS, Moscow, 119334 (Russian Federation)
2014-06-01
Combining Planck CMB temperature [1] and BICEP2 B-mode polarization data [2,3] we show qualitatively that, assuming inflationary consistency relation, the power-law form of the scalar primordial spectrum is ruled out at more than 3σ CL. This is an important finding, since the power-law form of the scalar primordial spectrum is one of the main assumptions of concordance model of cosmology and also a direct prediction of many inflationary scenarios. We show that a break or step in the form of the primordial scalar perturbation spectrum, similar to what we studied recently analyzing Planck data [4], can address both Planck and BICEP2 results simultaneously. Our findings also indicate that the data may require more flexibilities than what running of scalar spectral index can provide. Finally we show that an inflaton potential, originally appeared in [5], can generate both the step and the break model of scalar primordial spectrum in two different limits. The discussed potential is found to be favored by Planck data but marginally disfavored by BICEP2 results as it produces slightly lower amplitude of tensor primordial spectrum. Hence, if the tensor-to-scalar ratio (r) quoted by BICEP2 persists, it is of importance that we generate inflationary models with large r and at the same time provide suppression in scalar primordial spectrum at large scales.
Cole, Shaun; Percival, Will J.; Peacock, John A.; Norberg, Peder; Baugh, Carlton M.; Frenk, Carlos S.; Baldry, Ivan; Bland-Hawthorn, Joss; Bridges, Terry; Cannon, Russell; Colless, Matthew; Collins, Chris; Couch, Warrick; Cross, Nicholas J. G.; Dalton, Gavin; Eke, Vincent R.; De Propris, Roberto; Driver, Simon P.; Efstathiou, George; Ellis, Richard S.; Glazebrook, Karl; Jackson, Carole; Jenkins, Adrian; Lahav, Ofer; Lewis, Ian; Lumsden, Stuart; Maddox, Steve; Madgwick, Darren; Peterson, Bruce A.; Sutherland, Will; Taylor, Keith
2005-09-01
We present a power-spectrum analysis of the final 2dF Galaxy Redshift Survey (2dFGRS), employing a direct Fourier method. The sample used comprises 221414 galaxies with measured redshifts. We investigate in detail the modelling of the sample selection, improving on previous treatments in a number of respects. A new angular mask is derived, based on revisions to the photometric calibration. The redshift selection function is determined by dividing the survey according to rest-frame colour, and deducing a self-consistent treatment of k-corrections and evolution for each population. The covariance matrix for the power-spectrum estimates is determined using two different approaches to the construction of mock surveys, which are used to demonstrate that the input cosmological model can be correctly recovered. We discuss in detail the possible differences between the galaxy and mass power spectra, and treat these using simulations, analytic models and a hybrid empirical approach. Based on these investigations, we are confident that the 2dFGRS power spectrum can be used to infer the matter content of the universe. On large scales, our estimated power spectrum shows evidence for the `baryon oscillations' that are predicted in cold dark matter (CDM) models. Fitting to a CDM model, assuming a primordial ns= 1 spectrum, h= 0.72 and negligible neutrino mass, the preferred parameters are Ωmh= 0.168 +/- 0.016 and a baryon fraction Ωb/Ωm= 0.185 +/- 0.046 (1σ errors). The value of Ωmh is 1σ lower than the 0.20 +/- 0.03 in our 2001 analysis of the partially complete 2dFGRS. This shift is largely due to the signal from the newly sampled regions of space, rather than the refinements in the treatment of observational selection. This analysis therefore implies a density significantly below the standard Ωm= 0.3: in combination with cosmic microwave background (CMB) data from the Wilkinson Microwave Anisotropy Probe (WMAP), we infer Ωm= 0.231 +/- 0.021.
Anisotropic power spectrum of refractive-index fluctuation in hypersonic turbulence.
Li, Jiangting; Yang, Shaofei; Guo, Lixin; Cheng, Mingjian
2016-11-10
An anisotropic power spectrum of the refractive-index fluctuation in hypersonic turbulence was obtained by processing the experimental image of the hypersonic plasma sheath and transforming the generalized anisotropic von Kármán spectrum. The power spectrum suggested here can provide as good a fit to measured spectrum data for hypersonic turbulence as that recorded from the nano-planar laser scattering image. Based on the newfound anisotropic hypersonic turbulence power spectrum, Rytov approximation was employed to establish the wave structure function and the spatial coherence radius model of electromagnetic beam propagation in hypersonic turbulence. Enhancing the anisotropy characteristics of the hypersonic turbulence led to a significant improvement in the propagation performance of electromagnetic beams in hypersonic plasma sheath. The influence of hypersonic turbulence on electromagnetic beams increases with the increase of variance of the refractive-index fluctuation and the decrease of turbulence outer scale and anisotropy parameters. The spatial coherence radius was much smaller than that in atmospheric turbulence. These results are fundamental to understanding electromagnetic wave propagation in hypersonic turbulence.
Energy Technology Data Exchange (ETDEWEB)
Tieliewuhan, E. [Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8553 (Japan); Ivannikov, A. [Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8553 (Japan) and Medical Radiological Research Center of RAMS, Korolyov str., 4, Obninsk 249036 (Russian Federation)]. E-mail: ivann@mail.ru; Zhumadilov, K. [Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8553 (Japan); Nalapko, M. [Medical Radiological Research Center of RAMS, Korolyov str., 4, Obninsk 249036 (Russian Federation); Tikunov, D. [Medical Radiological Research Center of RAMS, Korolyov str., 4, Obninsk 249036 (Russian Federation); Skvortsov, V. [Medical Radiological Research Center of RAMS, Korolyov str., 4, Obninsk 249036 (Russian Federation); Stepanenko, V. [Medical Radiological Research Center of RAMS, Korolyov str., 4, Obninsk 249036 (Russian Federation); Toyoda, S. [Department of Applied Physics, Okayama University of Science, 1-1 Ridai, Okayama 700-0005 (Japan); Tanaka, K. [Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8553 (Japan); Endo, S. [Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8553 (Japan); Hoshi, M. [Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3, Kasumi, Minami-ku, Hiroshima 734-8553 (Japan)
2006-04-15
Variation of the electron paramagnetic resonance (EPR) spectrum of the human tooth enamel recorded at different microwave power is investigated. The analytical models describing the native and the radiation-induced signals in the enamel are proposed, which fit the experimental spectra in wide range of microwave power. These models are designed to use for processing the spectra of irradiated enamel at determination of the absorbed dose from the intensity of the radiation-induced signal.
Probing reionization with the cross-power spectrum of 21 cm and near-infrared radiation backgrounds
Energy Technology Data Exchange (ETDEWEB)
Mao, Xiao-Chun, E-mail: xcmao@bao.ac.cn [National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012 (China)
2014-08-01
The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared (NIR) background light from high-redshift galaxies promises to be a powerful probe of cosmic reionization. In this paper, we investigate the cross-power spectrum during the epoch of reionization. We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model: metal-free stars and metal-poor stars. The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements. Then, the intensity of the NIR background is estimated by collecting emission from stars in first-light galaxies. On large scales, we find that the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization. However, these two radiation backgrounds quickly become anti-correlated as reionization proceeds. The maximum absolute value of the cross-power spectrum is |Δ{sub 21,NIR}{sup 2}|∼10{sup −4} mK nW m{sup –2} sr{sup –1}, reached at ℓ ∼ 1000 when the mean fraction of ionized hydrogen is x-bar{sub i}∼0.9. We find that Square Kilometer Array can measure the 21 cm-NIR cross-power spectrum in conjunction with mild extensions to the existing CIBER survey, provided that the integration time independently adds up to 1000 and 1 hr for 21 cm and NIR observations, and that the sky coverage fraction of the CIBER survey is extended from 4 × 10{sup –4} to 0.1. Measuring the cross-correlation signal as a function of redshift provides valuable information on reionization and helps confirm the origin of the 'missing' NIR background.
Probing Reionization with the Cross-power Spectrum of 21 cm and Near-infrared Radiation Backgrounds
Mao, Xiao-Chun
2014-08-01
The cross-correlation between the 21 cm emission from the high-redshift intergalactic medium and the near-infrared (NIR) background light from high-redshift galaxies promises to be a powerful probe of cosmic reionization. In this paper, we investigate the cross-power spectrum during the epoch of reionization. We employ an improved halo approach to derive the distribution of the density field and consider two stellar populations in the star formation model: metal-free stars and metal-poor stars. The reionization history is further generated to be consistent with the electron-scattering optical depth from cosmic microwave background measurements. Then, the intensity of the NIR background is estimated by collecting emission from stars in first-light galaxies. On large scales, we find that the 21 cm and NIR radiation backgrounds are positively correlated during the very early stages of reionization. However, these two radiation backgrounds quickly become anti-correlated as reionization proceeds. The maximum absolute value of the cross-power spectrum is |\\Delta ^2_{21,NIR}|\\sim 10^{-4} mK nW m-2 sr-1, reached at l ~ 1000 when the mean fraction of ionized hydrogen is \\bar{x}_{i}\\sim 0.9. We find that Square Kilometer Array can measure the 21 cm-NIR cross-power spectrum in conjunction with mild extensions to the existing CIBER survey, provided that the integration time independently adds up to 1000 and 1 hr for 21 cm and NIR observations, and that the sky coverage fraction of the CIBER survey is extended from 4 × 10-4 to 0.1. Measuring the cross-correlation signal as a function of redshift provides valuable information on reionization and helps confirm the origin of the "missing" NIR background.
THE EFFECTS OF POLARIZED FOREGROUNDS ON 21 cm EPOCH OF REIONIZATION POWER SPECTRUM MEASUREMENTS
Energy Technology Data Exchange (ETDEWEB)
Moore, David F.; Aguirre, James E. [Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA (United States); Parsons, Aaron R.; Pober, Jonathan C. [Astronomy Department, University of California, Berkeley, Berkeley, CA (United States); Jacobs, Daniel C., E-mail: damo@sas.upenn.edu [School of Earth and Space Exploration, Arizona State University, Tempe, AZ USA (United States)
2013-06-01
Experiments aimed at detecting highly-redshifted 21 cm emission from the epoch of reionization (EoR) are plagued by the contamination of foreground emission. A potentially important source of contaminating foregrounds may be Faraday-rotated, polarized emission, which leaks into the estimate of the intrinsically unpolarized EoR signal. While these foregrounds' intrinsic polarization may not be problematic, the spectral structure introduced by the Faraday rotation could be. To better understand and characterize these effects, we present a simulation of the polarized sky between 120 and 180 MHz. We compute a single visibility, and estimate the three-dimensional power spectrum from that visibility using the delay spectrum approach presented in Parsons et al. Using the Donald C. Backer Precision Array to Probe the Epoch of Reionization as an example instrument, we show the expected leakage into the unpolarized power spectrum to be several orders of magnitude above the expected 21 cm EoR signal.
An ideal mass assignment scheme for measuring the Power Spectrum with FFTs
Cui, Weiguang; Yang, Xiaohu; Wang, Yu; Feng, Longlong; Springel, Volker
2008-01-01
In measuring the power spectrum of the distribution of large numbers of dark matter particles in simulations, or galaxies in observations, one has to use Fast Fourier Transforms (FFT) for calculational efficiency. However, because of the required mass assignment onto grid points in this method, the measured power spectrum $\\la |\\delta^f(k)|^2\\ra$ obtained with an FFT is not the true power spectrum $P(k)$ but instead one that is convolved with a window function $|W(\\vec k)|^2$ in Fourier space. In a recent paper, Jing (2005) proposed an elegant algorithm to deconvolve the sampling effects of the window function and to extract the true power spectrum, and tests using N-body simulations show that this algorithm works very well for the three most commonly used mass assignment functions, i.e., the Nearest Grid Point (NGP), the Cloud In Cell (CIC) and the Triangular Shaped Cloud (TSC) methods. In this paper, rather than trying to deconvolve the sampling effects of the window function, we propose to select a particu...
Determination of the Linear Mass Power Spectrum From the Mass Function of Galaxy Clusters
Sánchez, A G; Lambas, D G
2002-01-01
We develop a new method to determine the linear mass power spectrum using the mass function of galaxy clusters. We obtain the rms mass fluctuation sigma (M) using the expression for the mass function in the Press & Schechter (1974), Sheth, Mo & Tormen (2001) and Jenkins et al. (2001) formalisms. We apply different techniques to recover the adimensional power spectrum Delta ^{2}(k) from sigma (M) namely the k_{eff} approximation, the singular value decomposition and the linear regularization method. The application of these techniques to the tCDM and LCDM GIF simulations shows a high efficiency in recovering the theoretical power spectrum over a wide range of scales. We compare our results with those derived from the power spectrum of the spatial distribution of the same sample of clusters in the simulations obtained by application of the classical Feldman, Kaiser & Peacock (1994), FKP, method. We find that the mass function based method presented here can provide a very accurate estimate of the li...
Distance Dependent Model for the Delay Power Spectrum of In-room Radio Channels
DEFF Research Database (Denmark)
Steinböck, Gerhard; Pedersen, Troels; Fleury, Bernard Henri;
2013-01-01
A model based on experimental observations of the delay power spectrum in closed rooms is proposed. The model includes the distance between the transmitter and the receiver as a parameter which makes it suitable for range based radio localization. The experimental observations motivate the propos...
Slow-roll inflation and BB-mode angular power spectrum of CMB
Energy Technology Data Exchange (ETDEWEB)
Malsawmtluangi, N.; Suresh, P.K. [University of Hyderabad, School of Physics, Hyderabad (India)
2016-05-15
The BB-mode correlation angular power spectrum of CMB is obtained by considering the primordial gravitational waves in the squeezed vacuum state for various inflationary models and results are compared with the joint analysis of the BICEP2/Keck Array and Planck 353 GHz data. The present results may constrain several models of inflation. (orig.)
DEFF Research Database (Denmark)
Relano-Iborra, Helia; May, Tobias; Zaar, Johannes
-based Envelope Power Spectrum Model (mr-sEPSM) [2], combined with the correlation back-end of the Short-Time Objective Intelligibility measure (STOI) [3]. The sEPSMcorr can accurately predict NH data for a broad range of listening conditions, e.g., additive noise, phase jitter and ideal binary mask processing....
Planck 2013 results. XXI. All-sky Compton parameter power spectrum and high-order statistics
Ade, P.A.R.; Armitage-Caplan, C.; Arnaud, M.; Ashdown, M.; Atrio-Barandela, F.; Aumont, J.; Baccigalupi, C.; Banday, A.J.; Barreiro, R.B.; Bartlett, J.G.; Battaner, E.; Benabed, K.; Benoit, A.; Benoit-Levy, A.; Bernard, J.P.; Bersanelli, M.; Bielewicz, P.; Bobin, J.; Bock, J.J.; Bonaldi, A.; Bond, J.R.; Borrill, J.; Bouchet, F.R.; Bridges, M.; Bucher, M.; Burigana, C.; Butler, R.C.; Cardoso, J.F.; Carvalho, P.; Catalano, A.; Challinor, A.; Chamballu, A.; Chiang, L.Y.; Chiang, H.C.; Christensen, P.R.; Church, S.; Clements, D.L.; Colombi, S.; Colombo, L.P.L.; Comis, B.; Couchot, F.; Coulais, A.; Crill, B.P.; Curto, A.; Cuttaia, F.; Da Silva, A.; Danese, L.; Davies, R.D.; Davis, R.J.; de Bernardis, P.; de Rosa, A.; de Zotti, G.; Delabrouille, J.; Delouis, J.M.; Desert, F.X.; Dickinson, C.; Diego, J.M.; Dolag, K.; Dole, H.; Donzelli, S.; Dore, O.; Douspis, M.; Dupac, X.; Efstathiou, G.; Ensslin, T.A.; Eriksen, H.K.; Finelli, F.; Flores-Cacho, I.; Forni, O.; Frailis, M.; Franceschi, E.; Galeotta, S.; Ganga, K.; Genova-Santos, R.T.; Giard, M.; Giardino, G.; Giraud-Heraud, Y.; Gonzalez-Nuevo, J.; Gorski, K.M.; Gratton, S.; Gregorio, A.; Gruppuso, A.; Hansen, F.K.; Hanson, D.; Harrison, D.; Henrot-Versille, S.; Hernandez-Monteagudo, C.; Herranz, D.; Hildebrandt, S.R.; Hivon, E.; Hobson, M.; Holmes, W.A.; Hornstrup, A.; Hovest, W.; Huffenberger, K.M.; Hurier, G.; Jaffe, T.R.; Jaffe, A.H.; Jones, W.C.; Juvela, M.; Keihanen, E.; Keskitalo, R.; Kisner, T.S.; Kneissl, R.; Knoche, J.; Knox, L.; Kunz, M.; Kurki-Suonio, H.; Lacasa, F.; Lagache, G.; Lahteenmaki, A.; Lamarre, J.M.; Lasenby, A.; Laureijs, R.J.; Lawrence, C.R.; Leahy, J.P.; Leonardi, R.; Leon-Tavares, J.; Lesgourgues, J.; Liguori, M.; Lilje, P.B.; Linden-Vornle, M.; Lopez-Caniego, M.; Lubin, P.M.; Macias-Perez, J.F.; Maffei, B.; Maino, D.; Mandolesi, N.; Marcos-Caballero, A.; Maris, M.; Marshall, D.J.; Martin, P.G.; Martinez-Gonzalez, E.; Masi, S.; Matarrese, S.; Matthai, F.; Mazzotta, P.; Melchiorri, A.; Melin, J.B.; Mendes, L.; Mennella, A.; Migliaccio, M.; Mitra, S.; Miville-Deschenes, M.A.; Moneti, A.; Montier, L.; Morgante, G.; Mortlock, D.; Moss, A.; Munshi, D.; Naselsky, P.; Nati, F.; Natoli, P.; Netterfield, C.B.; Norgaard-Nielsen, H.U.; Noviello, F.; Novikov, D.; Novikov, I.; Osborne, S.; Oxborrow, C.A.; Paci, F.; Pagano, L.; Pajot, F.; Paoletti, D.; Partridge, B.; Pasian, F.; Patanchon, G.; Perdereau, O.; Perotto, L.; Perrotta, F.; Piacentini, F.; Piat, M.; Pierpaoli, E.; Pietrobon, D.; Plaszczynski, S.; Pointecouteau, E.; Polenta, G.; Ponthieu, N.; Popa, L.; Poutanen, T.; Pratt, G.W.; Prezeau, G.; Prunet, S.; Puget, J.L.; Rachen, J.P.; Rebolo, R.; Reinecke, M.; Remazeilles, M.; Renault, C.; Ricciardi, S.; Riller, T.; Ristorcelli, I.; Rocha, G.; Rosset, C.; Rossetti, M.; Roudier, G.; Rubino-Martin, J.A.; Rusholme, B.; Sandri, M.; Santos, D.; Savini, G.; Scott, D.; Seiffert, M.D.; Shellard, E.P.S.; Spencer, L.D.; Starck, J.L.; Stolyarov, V.; Stompor, R.; Sudiwala, R.; Sunyaev, R.; Sureau, F.; Sutton, D.; Suur-Uski, A.S.; Sygnet, J.F.; Tauber, J.A.; Tavagnacco, D.; Terenzi, L.; Toffolatti, L.; Tomasi, M.; Tristram, M.; Tucci, M.; Tuovinen, J.; Umana, G.; Valenziano, L.; Valiviita, J.; Van Tent, B.; Varis, J.; Vielva, P.; Villa, F.; Vittorio, N.; Wade, L.A.; Wandelt, B.D.; White, S.D.M.; Yvon, D.; Zacchei, A.; Zonca, A.
2014-01-01
We have constructed the first all-sky map of the thermal Sunyaev-Zeldovich (tSZ) effect by applying specifically tailored component separation algorithms to the 100 to 857 GHz frequency channel maps from the Planck survey. These maps show an obvious galaxy cluster tSZ signal that is well matched with blindly detected clusters in the Planck SZ catalogue. To characterize the signal in the tSZ map we have computed its angular power spectrum. At large angular scales ($\\ell 500$) the clustered Cosmic Infrared Background (CIB) and residual point sources are the major contaminants. These foregrounds are carefully modelled and subtracted. We measure the tSZ power spectrum in angular scales, $0.17^{\\circ} \\lesssim \\theta \\lesssim 3.0^{\\circ}$, that were previously unexplored. The measured tSZ power spectrum is consistent with that expected from the Planck catalogue of SZ sources, with additional clear evidence of signal from unresolved clusters and, potentially, diffuse warm baryons. We use the tSZ power spectrum to ...
First limits on the 21 cm power spectrum during the Epoch of X-ray heating
Ewall-Wice, A.; Dillon, Joshua S.; Hewitt, J. N.; Loeb, A.; Mesinger, A.; Neben, A. R.; Offringa, A. R.; Tegmark, M.; Barry, N.; Beardsley, A. P.; Bernardi, G.; Bowman, Judd D.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; de Oliveira-Costa, A.; Emrich, D.; Feng, L.; Gaensler, B. M.; Goeke, R.; Greenhill, L. J.; Hazelton, B. J.; Hurley-Walker, N.; Johnston-Hollitt, M.; Jacobs, Daniel C.; Kaplan, D. L.; Kasper, J. C.; Kim, HS; Kratzenberg, E.; Lenc, E.; Line, J.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morales, M. F.; Morgan, E.; Thyagarajan, Nithyanandan; Oberoi, D.; Ord, S. M.; Paul, S.; Pindor, B.; Pober, J. C.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Shankar, N. Udaya; Sethi, Shiv K.; Srivani, K. S.; Subrahmanyan, R.; Sullivan, I. S.; Tingay, S. J.; Trott, C. M.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wu, C.; Wyithe, J. S. B.
2016-01-01
We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). 3 h of observations were conducted over two nights with significantly diff
Evolution of the CMB Power Spectrum Across WMAP Data Releases: A Nonparametric Analysis
Aghamousa, Amir; Souradeep, Tarun
2011-01-01
We present a comparative analysis of the WMAP 1-, 3-, 5-, and 7-year data releases for the CMB angular power spectrum, with respect to the following three key questions: (a) How well is the angular power spectrum determined by the data alone? (b) How well is the Lambda-CDM model supported by a model-independent, data-driven analysis? (c) What are the realistic uncertainties on peak/dip locations and heights? Our analysis is based on a nonparametric function estimation methodology [1,2]. Our results show that the height of the power spectrum is well determined by data alone for multipole index l approximately less than 600 (1-year), 800 (3-year), and 900 (5- and 7-year data realizations). We also show that parametric fits based on the Lambda-CDM model are remarkably close to our nonparametric fit in l-regions where the data are sufficiently precise. A contrasting example is provided by an H-Lambda-CDM model: As the data become precise with successive data realizations, the H-Lambda-CDM angular power spectrum g...
Choi, Kwang-Ho; Cho, Seong Jin; Kang, Suk-Yun; Ahn, Seong Hun
2016-01-01
To identify physical and sensory responses to acupuncture point stimulation (APS), nonacupuncture point stimulation (NAPS) and no stimulation (NS), changes in the high-frequency power spectrum before and after stimulation were evaluated with electroencephalography (EEG). A total of 37 healthy subjects received APS at the LI4 point, NAPS, or NS with their eyes closed. Background brain waves were measured before, during, and after stimulation using 8 channels. Changes in the power spectra of gamma waves and high beta waves before, during, and after stimulation were comparatively analyzed. After NAPS, absolute high beta power (AHBP), relative high beta power (RHBP), absolute gamma power (AGP), and relative gamma power (RGP) tended to increase in all channels. But no consistent notable changes were found for APS and NS. NAPS is believed to cause temporary reactions to stress, tension, and sensory responses of the human body, while APS responds stably compared to stimulation of other parts of the body.
Directory of Open Access Journals (Sweden)
Kwang-Ho Choi
2016-01-01
Full Text Available To identify physical and sensory responses to acupuncture point stimulation (APS, nonacupuncture point stimulation (NAPS and no stimulation (NS, changes in the high-frequency power spectrum before and after stimulation were evaluated with electroencephalography (EEG. A total of 37 healthy subjects received APS at the LI4 point, NAPS, or NS with their eyes closed. Background brain waves were measured before, during, and after stimulation using 8 channels. Changes in the power spectra of gamma waves and high beta waves before, during, and after stimulation were comparatively analyzed. After NAPS, absolute high beta power (AHBP, relative high beta power (RHBP, absolute gamma power (AGP, and relative gamma power (RGP tended to increase in all channels. But no consistent notable changes were found for APS and NS. NAPS is believed to cause temporary reactions to stress, tension, and sensory responses of the human body, while APS responds stably compared to stimulation of other parts of the body.
Choi, Kwang-Ho; Kwon, O Sang; Cho, Seong Jin; Lee, Sanghun; Kang, Suk-Yun; Ahn, Seong Hun; Ryu, Yeonhee
2016-01-01
To identify physical and sensory responses to acupuncture point stimulation (APS), nonacupuncture point stimulation (NAPS) and no stimulation (NS), changes in the high-frequency power spectrum before and after stimulation were evaluated with electroencephalography (EEG). A total of 37 healthy subjects received APS at the LI4 point, NAPS, or NS with their eyes closed. Background brain waves were measured before, during, and after stimulation using 8 channels. Changes in the power spectra of gamma waves and high beta waves before, during, and after stimulation were comparatively analyzed. After NAPS, absolute high beta power (AHBP), relative high beta power (RHBP), absolute gamma power (AGP), and relative gamma power (RGP) tended to increase in all channels. But no consistent notable changes were found for APS and NS. NAPS is believed to cause temporary reactions to stress, tension, and sensory responses of the human body, while APS responds stably compared to stimulation of other parts of the body.
Predictions for the 21 cm-galaxy cross-power spectrum observable with LOFAR and Subaru
Vrbanec, Dijana; Ciardi, Benedetta; Jelić, Vibor; Jensen, Hannes; Zaroubi, Saleem; Fernandez, Elizabeth R.; Ghosh, Abhik; Iliev, Ilian T.; Kakiichi, Koki; Koopmans, Léon V. E.; Mellema, Garrelt
2016-03-01
The 21 cm-galaxy cross-power spectrum is expected to be one of the promising probes of the Epoch of Reionization (EoR), as it could offer information about the progress of reionization and the typical scale of ionized regions at different redshifts. With upcoming observations of 21 cm emission from the EoR with the Low Frequency Array (LOFAR), and of high-redshift Ly α emitters with Subaru's Hyper Suprime-Cam (HSC), we investigate the observability of such cross-power spectrum with these two instruments, which are both planning to observe the ELAIS-N1 field at z = 6.6. In this paper, we use N-body + radiative transfer (both for continuum and Ly α photons) simulations at redshift 6.68, 7.06 and 7.3 to compute the 3D theoretical 21 cm-galaxy cross-power spectrum and cross-correlation function, as well as to predict the 2D 21 cm-galaxy cross-power spectrum and cross-correlation function expected to be observed by LOFAR and HSC. Once noise and projection effects are accounted for, our predictions of the 21 cm-galaxy cross-power spectrum show clear anti-correlation on scales larger than ˜60 h-1 Mpc (corresponding to k ˜ 0.1 h Mpc-1), with levels of significance p = 0.003 at z = 6.6 and p = 0.08 at z = 7.3. On smaller scales, instead, the signal is completely contaminated. On the other hand, our 21 cm-galaxy cross-correlation function is strongly contaminated by noise on all scales, since the noise is no longer being separated by its k modes.
A High Power Density DC-DC Converter for Distributed PV Architectures
Energy Technology Data Exchange (ETDEWEB)
Agamy, Mohammed S; Chi, Song; Elasser, Ahmed; Harfman-Todorovic, Maja; Jiang, Yan; Mueller, Frank; Tao, Fengfeng
2012-06-01
In order to maximize solar energy harvesting capabilities, power converters have to be designed for high efficiency and good MPPT and voltage/current performance. When many converters are used in distributed systems, power density also becomes an important factor as it allows for simpler system integration. In this paper a high power density string dc-dc converter suitable for distributed medium to large scale PV installation is presented. A simple partial power processing topology, implemented with all silicon carbide devices provides high efficiency as well as high power density. A 3.5kW, 100kHz converter is designed and tested to verify the proposed methods.
Institute of Scientific and Technical Information of China (English)
YANG; Xiaohu
2001-01-01
［1］Vogeley, M. S., Szalay, A. S., Eigenmode analysis of galaxy redsh ift surveys. I. theory and methods, ApJ, 1996, 465: 34-53.［2］Fang, L. Z., Pando, J., Large-scale structures revealed by wavel et decomposition, The 5th Current Topics of Astrofundamental Physics (eds. Sanch ez, N., Zichichi, A.), Singapore: World Scientific, 1997.［3］Pando, J., Fang, L. Z., Detecting the non-Gaussian spectrum of Q SO's Lyalpha absorption line distribution, A&A, 1998, 340: 335-342.［4］Xu, W., Fang, L. Z., Deng, Z. G., Scale invariance of rich cluste r abundance: A possible test for models of structure formation, ApJ, 1998, 508: 472-482.［5］Pando, J., Valls-Gabaud, D., Fang, L. Z., Evidence for scale-sc ale correlations in the cosmic microwave background radiation, PRL, 1998, 81: 45 68-4571.［6］Feng, L. L., Fang, L. Z., Non-Gaussianity and the recovery of th e mass power spectrum from the Lyα forest, ApJ, 2000, 535: 519-529.［7］Feng, L. L., Deng, Z. G., Fang, L. Z., Breaking degeneracy of dar k matter models by the scale-scale correlations of galaxies, ApJ, 2000, 530: 53 -61.［8］Fang, L. Z., Feng, L. L., Measuring the galaxy power spectrum and scale-scale correlations with multiresolution-decomposed covariance-I. metho d, ApJ, 2000, 539: 9-22.［9］Tegmark, M., Hamilton, A. J. S., Vogeley, M. S. et al., Measuring the galaxy power spectrum with future redshift surveys, ApJ, 1998, 499: 555-57 6.［10］Bardeen, J. M., Bond, J. R., Kaiser, N. et al., The statistics of peak s of Gauss random fields, ApJ, 1986, 304: 15-61.［11］Peacock, J. A., Dodds, S. J., Linear power spectrum of cosmological ma ss fluctuations, MNRAS, 1994, 267: 1020-1034.［12］White, S. D. M., Efstathiou, G., Frenk, C. S., The amplitude of mass f luctuations in the universe, MNRAS, 1993, 262: 1023-1028.［13］Peacock, J. A., Dodds, S. J., Non-linear evolution of cosmological po wer spectra, MNRAS, 1996, 280: L19-L26.［14］Loveday, J., Peterson, B. A., Efstathiou, G. et al., The
OXIDATION OF DRY HYDROCARBONS AT HIGH-POWER DENSITY ANODES
Energy Technology Data Exchange (ETDEWEB)
K.Krist; O. Spaldon-Stewart; R. Remick
2004-03-01
performance life on dry methane with sulfur compounds was much longer than with dry methane alone. The effect of sulfur compounds in these cases appeared to correlate with inhibition of carbon deposition. Mixed results were obtained for the effect of the sulfur compounds on power density. Progress also was made in understanding the mechanisms involved in direct utilization of dry natural gas. Evidence was developed for three possible mechanisms for dry methane utilization in addition to the usually cited mechanism--direct oxidation of methane by oxygen anions. Further work is required at a fundamental level before the knowledge gained here can be translated into higher levels of performance.
DEFF Research Database (Denmark)
Sørensen, Simon Toft; Larsen, Casper; Møller, Uffe;
2012-01-01
The noise properties of a supercontiuum can be significantly improved both in terms of coherence and intensity stability by modulating the input pulse with a seed. In this paper, we numerically investigate the influence of the seed wavelength, the pump power, and the modulation instability gain...... spectrum. Finally, we show that the coherent pulse breakup afforded by seeding is washed out by turbulent solitonic dynamics when the pump power is increased to the kilowatt level. Thus our results show that seeding cannot improve the noise performance of a high power supercontinuum source....
The Non-Linear Power Spectrum of the Lyman Alpha Forest
Arinyo-i-Prats, Andreu; Viel, Matteo; Cen, Renyue
2015-01-01
The Lyman alpha forest power spectrum has been measured on large scales by the BOSS survey in SDSS-III at $z\\sim 2.3$, has been shown to agree well with linear theory predictions, and has provided the first measurement of Baryon Acoustic Oscillations at this redshift. However, the power at small scales, affected by non-linearities, has not been well examined so far. We present results from a variety of hydrodynamic simulations to predict the redshift space non-linear power spectrum of the Lyman Alpha transmission for several models, testing the dependence on resolution and box size. A new fitting formula is introduced to facilitate the comparison of our simulation results with observations and other simulations. The non-linear power spectrum has a generic shape determined by a transition scale from linear to non-linear anisotropy, and a Jeans scale below which the power drops rapidly. In addition, we predict the two linear bias factors of the Lyman Alpha forest and provide a better physical interpretation of ...
Baryon oscillations in galaxy and matter power-spectrum covariance matrices
Neyrinck, Mark C
2007-01-01
We investigate large-amplitude baryon acoustic oscillations (BAO's) in off-diagonal entries of cosmological power-spectrum covariance matrices. These covariance-matrix BAO's describe the increased attenuation of power-spectrum BAO's caused by upward fluctuations in large-scale power. We derive an analytic approximation to covariance-matrix entries in the BAO regime, and check the analytical predictions using N-body simulations. These BAO's look much stronger than the BAO's in the power spectrum, but seem detectable only at about a one-sigma level in gigaparsec-scale galaxy surveys. In estimating cosmological parameters using matter or galaxy power spectra, including the covariance-matrix BAO's can have a several-percent effect on error-bar widths for some parameters directly related to the BAO's, such as the baryon fraction. Also, we find that including the numerous galaxies in small haloes in a survey can reduce error bars in these cosmological parameters more than the simple reduction in shot noise might su...
Power spectrum of the cosmic infrared background at 60 and 100 microns with IRAS
Miville-Deschênes, M A; Puget, J L
2002-01-01
Based on a power spectrum analysis of the IRAS ISSA maps, we present the first detection of the Cosmic far-Infrared Background (CIB) fluctuations at 60 and 100 microns. The power spectrum of 12 low cirrus emission regions is characterized by a power excess at spatial frequencies higher than k~0.02 arcmin^{-1}. Most of this excess is due to noise and to nearby point sources with a flux stronger than 1 Jy. But we show that when these contributions are carefully removed, there is still a power excess that is the signature of the CIB fluctuations. The power spectrum of the CIB at 60 and 100 microns is compatible with a Poissonian distribution, at spatial frequencies between 0.025 and 0.2 arcmin^{-1}. The fluctuation level is ~1.6x10^3 Jy^2/sr and ~5.8x10^3 Jy^2/sr at 60 and 100 microns respectively. The levels of the fluctuations are used in a larger framework, with other observationnal data, to constrain the evolution of IR galaxies (Lagache et al. 2002). The detections reported here, coupled with the level of t...
The effects of galaxy formation on the matter power spectrum: A challenge for precision cosmology
van Daalen, Marcel P; Booth, C M; Vecchia, Claudio Dalla
2011-01-01
Upcoming weak lensing surveys, such as LSST, EUCLID, and WFIRST, aim to measure the matter power spectrum with unprecedented accuracy. In order to fully exploit these observations, models are needed that, given a set of cosmological parameters, can predict the non-linear matter power spectrum at the level of 1% or better for scales corresponding to comoving wave numbers 0.170 h/Mpc. Therefore, baryons, and particularly AGN feedback, cannot be ignored in theoretical power spectra for k>0.3 h/Mpc. It will thus be necessary to improve our understanding of feedback processes in galaxy formation, or at least to constrain them through auxiliary observations, before we can fulfil the goals of upcoming weak lensing surveys.
Kim, Jaiseung
2010-01-01
We have investigated the odd-parity preference of the WMAP 7 year power spectrum. Our investigation shows parity asymmetry of the WMAP data (2<= l <=22) is anomalous at 4-in-1000 level. We also find it likely that low quadrupole power is part of this parity asymmetry rather than an isolated anomaly. We have investigated non-cosmological causes for the odd-parity preference, but have not found a definite non-cosmological origin. WMAP7 data possesses most anomalous odd-parity preference, while they have more accurate calibration and less foreground contamination than earlier data. Besides that, the anomaly is associated with the WMAP power spectrum data, in which most efforts have been exerted to minimize systematics. Therefore, we find it unlikely that calibration or foregrounds are the source of the anomaly. We have also considered primordial origin for the parity asymmetry. However, we find primordial origin requires violation of translational invariance on large scales.
Energy Technology Data Exchange (ETDEWEB)
Lundstrom, Blake [National Renewable Energy Lab. (NREL), Golden, CO (United States)
2017-05-08
Google is encouraging development of advanced photovoltaic inverters with high power density by holding a public competition and offering a prize for the best performing high power developed. NREL will perform the performance and validation for all inverters entered into the competition and provide results to Google.
Isocurvature and curvaton perturbations with red power spectrum and large hemispherical asymmetry
Energy Technology Data Exchange (ETDEWEB)
McDonald, John, E-mail: j.mcdonald@lancaster.ac.uk [Lancaster-Manchester-Sheffield Consortium for Fundamental Physics, Cosmology and Astroparticle Physics Group, Dept. of Physics, University of Lancaster, Lancaster LA1 4YB (United Kingdom)
2013-07-01
We calculate the power spectrum and hemispherical asymmetry of isocurvature and curvaton perturbations due to a complex field Φ which is evolving along the tachyonic part of its potential. Using a semi-classical evolution of initially sub-horizon quantum fluctuations, we compute the power spectrum, mean field and hemispherical asymmetry as a function of the number of e-foldings of tachyonic growth ΔN and the tachyonic mass term cH{sup 2}. We find that a large hemispherical asymmetry due to the modulation of |Φ| can easily be generated via the spatial modulation of |Φ| across the horizon, with Δ|Φ|/|Φ| > 0.5 when the observed Universe exits the horizon within 10-40 e-foldings of the beginning of tachyonic evolution and c is in the range 0.1-1. The spectral index of the isocurvature and curvaton perturbations is generally negative, corresponding to a red power spectrum. Dark matter isocurvature perturbations due to an axion-like curvaton with a large hemispherical asymmetry may be able to explain the hemispherical asymmetry observed by WMAP and Planck. In this case, the red spectrum can additionally suppress the hemispherical asymmetry at small scales, which should make it easier to satisfy scale-dependence requirements on the asymmetry from quasar number counts.
Probing the Scale Invariance of the Inflationary Power Spectrum in Expanding Dipolar Condensates
Chä, Seok-Yeong
2016-01-01
We consider an analogue de Sitter cosmos in an expanding quasi-two-dimensional Bose-Einstein condensate, with dominant dipole-dipole interactions between the atoms or molecules in the ultracold gas. It is demonstrated that a hallmark signature of inflationary cosmology, the scale invariance of the power spectrum of inflaton field correlations, experiences strong modifications when at the initial stage of expansion the excitation spectrum displays a roton minimum. Dipolar quantum gases thus furnish a viable laboratory tool to experimentally investigate, with well-defined and controllable initial conditions, whether primordial oscillation spectra deviating from Lorentz invariance at trans-Planckian momenta violate standard predictions of inflationary cosmology.
JPL 2-to-the-20th-power channel 300 MHz bandwidth digital spectrum analyzer
Morris, G. A., Jr.; Wilck, H. C.
1978-01-01
A million (two to the 20th power) channel, 300 MHz bandwidth, digital spectrum analyzer was considered. The design, fabrication, and maintenance philosophy of the modular, pipelined, fast fourier transform (FFT) hardware are described. The spectrum analyzer will be used to examine the region from 1.4 GHz to 26 GHz for radio frequency interference which may be harmful to present and future tracking missions of the Deep Space Network. The design has application to the search for extraterrestrial intelligence signals and radio science phenomena.
Three-Phase PWM Power Conversion--The Route to Ultra High Power Density and Efficiency
Institute of Scientific and Technical Information of China (English)
J W Kolar; J Minib(o)ck; T Nussbaumer
2005-01-01
A review of three-phase PWM converter topologies which do show a low complexity/high reliability and high efficiency and power density and are therefore of main interest for a future industrial application is presented.A three-switch/level Boost-type PWM rectifier (VIENNA Rectifier),a Buck+Boost-type PWM rectifier with wide output voltage range and the AC/AC Sparse Matrix Converter concept are discussed in detail and topics to be treated in the course of further research are identified. Finally,it is shown how the aspects being relevant for the realization of highly compact converter systems could be integrated into education in the field.
Sound power spectrum and wave drag of a propeller in flight
Hanson, D. B.
1989-01-01
Theory is presented for the sound power and sound power spectrum of a single rotation propeller in forward flight. Calculations are based on the linear wave equation with sources distributed over helicoidal surfaces to represent effects of blade thickness and steady loading. Sound power is distributed continuously over frequecy, as would be expected from Doppler effects, rather than in discrete harmonics. The theory is applied to study effects of sweep and Mach number in propfans. An acoustic efficiency is defined as the ratio of radiated sound power to shaft input power. This value is the linear estimate of the effect of wave drag due to the supersonic blade section speeds. It is shown that the acoustic efficiency is somewhat less than 1 percent for a well designed propfan.
The DWT Power Spectrum of the two-degree Field Galaxy Redshift Survey
Cai, Y C; Zhao, Y H; Feng, L L; Fang, L Z; Cai, Yan-Chuan; Pan, Jun; Zhao, Yong-Heng; Feng, Long-Long; Fang, Li-Zhi
2006-01-01
The power spectrum of the two-degree Field Galaxy Redshift Survey (2dFGRS) sample is estimated with the discrete wavelet transform (DWT) method. The DWT power spectra within $0.04
Das, Sudeep; Nolta, Michael R; Addison, Graeme E; Battistelli, Elia S; Bond, J Richard; Calabrese, Erminia; Devlin, Devin Crichton Mark J; Dicker, Simon; Dunkley, Joanna; Dünner, Rolando; Fowler, Joseph W; Gralla, Megan; Hajian, Amir; Halpern, Mark; Hasselfield, Matthew; Hilton, Matt; Hincks, Adam D; Hlozek, Renée; Huffenberger, Kevin M; Hughes, John P; Irwin, Kent D; Kosowsky, Arthur; Lupton, Robert H; Marriage, Tobias A; Marsden, Danica; Menanteau, Felipe; Moodley, Kavilan; Niemack, Michael D; Page, Lyman A; Partridge, Bruce; Reese, Erik D; Schmitt, Benjamin L; Sehgal, Neelima; Sherwin, Blake D; Sievers, Jonathan L; Spergel, David N; Staggs, Suzanne T; Swetz, Daniel S; Switzer, Eric R; Thornton, Robert; Trac, Hy; Wollack, Ed
2013-01-01
We present the temperature power spectra of the cosmic microwave background (CMB) derived from the three seasons of data from the Atacama Cosmology Telescope (ACT) at 148 GHz and 218 GHz, as well as the cross-frequency spectrum between the two channels. We detect and correct for contamination due to the Galactic cirrus in our equatorial maps. We present the results of a number of tests for possible systematic error and conclude that any effects are not significant compared to the statistical errors we quote. Where they overlap, we cross-correlate the ACT and the South Pole Telescope (SPT) maps and show they are consistent. The measurements of higher-order peaks in the CMB power spectrum provide an additional test of the Lambda CDM cosmological model, and help constrain extensions beyond the standard model. The small angular scale power spectrum also provides constraining power on the Sunyaev-Zel'dovich effects and extragalactic foregrounds. We also present a measurement of the CMB gravitational lensing conver...
Sunyaev-Zel'dovich power spectrum with decaying cold dark matter
Takahashi, K; Ichiki, K; Takahashi, Keitaro; Oguri, Masamune; Ichiki, Kiyotomo
2003-01-01
Recent studies of structures of galaxies and clusters imply that dark matter might be unstable and decay with lifetime $\\Gamma^{-1}$ about the age of universe. We study the effects of the decay of cold dark matter on the Sunyaev-Zel'dovich (SZ) power spectrum. We analytically calculate the SZ power spectrum taking finite lifetime of cold dark matter into account. We find the finite lifetime of dark matter decreases the power at large scale ($l 4000$). This is in marked contrast with the dependence of other cosmological parameters such as the amplitude of mass fluctuations $\\sigma_{8}$ and the cosmological constant $\\Omega_{\\lambda}$ (under the assumption of a flat universe) which mainly change the normalization of the angular power spectrum. This difference allows one to determine the lifetime and other cosmological parameters rather separately. We also investigate sensitivity of a future SZ survey to the cosmological parameters including the life time, assuming a fiducial model $\\Gamma^{-1} = 10 h^{-1} {\\rm...
Observational estimates of the initial power spectrum at small scale from Lyman-$\\alpha$ absorbers
Demianski, M
2003-01-01
We present a new method of measuring the power spectrum of initial perturbations to an unprecedently small scale of $\\sim$ 10$h^{-1}$ kpc. We apply this method to a sample of 4500 Ly-$\\alpha$ absorbers and recover the cold dark matter (CDM) like power spectrum at scales $\\geq 300h^{-1}$kpc with a precision of $\\sim$ 10%. However at scales $\\sim 10 - 300 h^{-1}$kpc the measured and CDM--like spectra are noticeable different. This result suggests a complex inflation with generation of excess power at small scales. The magnitude and reliability of these deviations depend also upon the possible incompleteness of our sample and poorly understood process of formation of weak absorbers. Confirmation of the CDM--like shape of the initial power spectrum or detection of its distortions at small scales are equally important for widely discussed problems of physics of the early Universe, galaxy formation, and reheating of the Universe. Our method links the observed mass function of absorbers with the correlation function...
Power spectrum extraction for redshifted 21-cm epoch of reionization experiments: the LOFAR case
Harker, Geraint; Bernardi, Gianni; Brentjens, Michiel A; de Bruyn, A G; Ciardi, Benedetta; Jelic, Vibor; Koopmans, Leon V E; Labropoulos, Panagiotis; Mellema, Garrelt; Offringa, Andre; Pandey, V N; Pawlik, Andreas H; Schaye, Joop; Thomas, Rajat M; Yatawatta, Sarod
2010-01-01
One of the aims of the Low Frequency Array (LOFAR) Epoch of Reionization (EoR) project is to measure the power spectrum of variations in the intensity of redshifted 21-cm radiation from the EoR. The sensitivity with which this power spectrum can be estimated depends on the level of thermal noise and sample variance, and also on the systematic errors arising from the extraction process, in particular from the subtraction of foreground contamination. We model the extraction process using realistic simulations of the cosmological signal, the foregrounds and noise, and so estimate the sensitivity of the LOFAR EoR experiment to the redshifted 21-cm power spectrum. Detection of emission from the EoR should be possible within 360 hours of observation with a single station beam. Integrating for longer, and synthesizing multiple station beams within the primary (tile) beam, then enables us to extract progressively more accurate estimates of the power at a greater range of scales and redshifts. We discuss different obs...
First Limits on the 21 cm Power Spectrum during the Epoch of X-ray heating
Ewall-Wice, A; Hewitt, J N; Loeb, A; Mesinger, A; Neben, A R; Offringa, A R; Tegmark, M; Barry, N; Beardsley, A P; Bernardi, G; Bowman, Judd D; Briggs, F; Cappallo, R J; Carroll, P; Corey, B E; de Oliveira-Costa, A; Emrich, D; Feng, L; Gaensler, B M; Goeke, R; Greenhill, L J; Hazelton, B J; Hurley-Walker, N; Johnston-Hollit, M; Jacobs, Daniel C; Kaplan, D L; Kasper, J C; Kim, HS; Kratzenberg, E; Lenc, E; Line, J; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morales, M F; Morgan, E; Thyagarajan, Nithyanandan; Oberoi, D; Ord, S M; Paul, S; Pindor, B; Pober, J C; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Sullivan, I S; Tingay, S J; Trott, C M; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wu, C; Wyithe, J S B
2016-01-01
We present first results from radio observations with the Murchison Widefield Array seeking to constrain the power spectrum of 21 cm brightness temperature fluctuations between the redshifts of 11.6 and 17.9 (113 and 75 MHz). Three hours of observations were conducted over two nights with significantly different levels of ionospheric activity. We use these data to assess the impact of systematic errors at low frequency, including the ionosphere and radio-frequency interference, on a power spectrum measurement. We find that after the 1-3 hours of integration presented here, our measurements at the Murchison Radio Observatory are not limited by RFI, even within the FM band, and that the ionosphere does not appear to affect the level of power in the modes that we expect to be sensitive to cosmology. Power spectrum detections, inconsistent with noise, due to fine spectral structure imprinted on the foregrounds by reflections in the signal-chain, occupy the spatial Fourier modes where we would otherwise be most se...
Multi-redshift limits on the 21cm power spectrum from PAPER
Pober, Daniel C Jacobs Jonathan C; Aguirre, James E; Ali, Zaki; Bowman, Judd; Bradley, Richard F; Carilli, Chris L; DeBoer, David R; Dexter, Matthew R; Gugliucci, Nicole E; Klima, Pat; Liu, Adrian; MacMahon, Dave H E; Manley, Jason R; Moore, David F; Stefan, Irina I; Walbrugh, William P
2014-01-01
The epoch of reionization power spectrum is expected to evolve strongly with redshift, and it is this variation with cosmic history that will allow us to begin to place constraints on the physics of reionization. The primary obstacle to the measurement of the EoR power spectrum is bright foreground emission. We present an analysis of observations from the Donald C. Backer Precision Array for Probing the Epoch of Reionization (PAPER) telescope which place new limits on the HI power spectrum over the redshift range of $7.5
Schmittfull, Marcel
2016-01-01
Modeling the large-scale structure of the universe on nonlinear scales has the potential to substantially increase the science return of upcoming surveys by increasing the number of modes available for model comparisons. One way to achieve this is to model nonlinear scales perturbatively. Unfortunately, this involves high-dimensional loop integrals that are cumbersome to evaluate. Trying to simplify this, we show how all 2-loop (next-to-next-to-leading order) corrections to the density power spectrum can be reduced to one-dimensional, radial integrals. Each of those can be evaluated with a one-dimensional Fast Fourier Transform. This provides a way to evaluate the 2-loop power spectrum using only one-dimensional Fast Fourier Transforms, which is significantly faster than the five-dimensional Monte-Carlo integrals that are needed otherwise. The general idea of this FFT-PT method is to change between Fourier and position space to avoid convolutions, integrate over orientations, and evaluate the remaining radial...
Reduced-density-matrix spectrum and block entropy of permutationally invariant many-body systems.
Salerno, Mario; Popkov, Vladislav
2010-07-01
Spectral properties of the reduced density matrix (RDM) of permutational invariant quantum many-body systems are investigated. The RDM block diagonalization which accounts for all symmetries of the Hamiltonian is achieved. The analytical expression of the RDM spectrum is provided for arbitrary parameters and rigorously proved in the thermodynamical limit. The existence of several sum rules and recurrence relations among RDM eigenvalues is also demonstrated and the distribution function of RDM eigenvalues (including degeneracies) characterized. In particular, we prove that the distribution function approaches a two-dimensional Gaussian in the limit of large subsystem sizes n>1. As a physical application we discuss the von Neumann entropy (VNE) of a block of size n for a system of hard-core bosons on a complete graph, as a function of n and of the temperature T. The occurrence of a crossover of VNE from purely logarithmic behavior at T=0 to a purely linear behavior in n for T≥Tc, is demonstrated.
Energy Technology Data Exchange (ETDEWEB)
Lingen Chen; Junlin Zheng; Fengrui Sun [Naval Univ. of Engineering, Faculty 306, Wuhan (China); Chih Wu [U.S. Naval Academy, Mechanical Engineering Dept., Annapolis, MD (United States)
2001-02-07
In this paper, the power density (defined as the ratio of the power output to the maximum specific volume in the cycle) is taken as the objective for performance optimisations of an endoreversible closed Brayton cycle coupled to constant-temperature heat reservoirs in the viewpoint of finite-time thermodynamics (FTT) or entropy generation minimisation (EGM). The optimum heat conductance distribution corresponding to the optimum power density of the hot- and cold-side heat exchangers for the fixed heat exchanger inventory is analysed using numerical examples. The influence of some design parameters on the optimum heat conductance distribution and the maximum power density and the optimum pressure ratio corresponding to the maximum power density are provided. The power plant design with optimisation leads to higher efficiency and smaller size. (Author)
Roke, Y.; Harten, P.N. van; Buitelaar, J.K.; Tenback, D.E.; Quekel, L.G.; Rijke, Y.B. de; Boot, A.M.
2012-01-01
OBJECTIVE: To investigate the long-term effects of antipsychotic (AP) treatment and AP-induced hyperprolactinemia on bone mineral density (BMD) and body composition in male adolescents with autism spectrum disorders (ASDs) and/or disruptive behavior disorder (DBD). DESIGN: Physically healthy 10- to
Y. Roke (Yvette); P.N. van Harten (Peter); J.K. Buitelaar (Jan); D.E. Tenback (Diederik); L.G.B.A. Quekel (Lorentz G. B.); Y.B. de Rijke (Yolanda); A.M. Boot (Annemieke)
2012-01-01
textabstractObjective: To investigate the long-term effects of antipsychotic (AP) treatment and AP-induced hyperprolactinemia on bone mineral density (BMD) and body composition in male adolescents with autism spectrum disorders (ASDs) and/or disruptive behavior disorder (DBD). Design: Physically hea
Roke, Yvette; van Harten, Peter N.; Buitelaar, Jan K.; Tenback, Diederik E.; Quekel, Lorentz G. B. A.; de Rijke, Yolanda B.; Boot, Annemieke M.
2012-01-01
Objective: To investigate the long-term effects of antipsychotic (AP) treatment and AP-induced hyperprolactinemia on bone mineral density (BMD) and body composition in male adolescents with autism spectrum disorders (ASDs) and/or disruptive behavior disorder (DBD). Design: Physically healthy 10- to
Lacot, Eric; Girardeau, Vadim; Hugon, Olivier; Jacquin, Olivier
2016-01-01
In this article, we study the non-linear coupling between the stationary (i.e. the beating modulation signal) and transient (i.e. the laser quantum noise) dynamics of a laser subjected to frequency shifted optical feedback. We show how the noise power spectrum and more specifically the relaxation oscillation frequency of the laser are modified under different optical feedback condition. Specifically we study the influence of (i) the amount of light returning to the laser cavity and (ii) the initial detuning between the frequency shift and intrinsic relaxation frequency. The present work shows how the relaxation frequency is related to the strength of the beating signal and the shape of the noise power spectrum gives an image of the Transfer Modulation Function (i.e. of the amplification gain) of the nonlinear-laser dynamics.The theoretical predictions, confirmed by numerical resolutions, are in good agreements with the experimental data.
CMBR Weak Lensing and HI 21-cm Cross-correlation Angular Power Spectrum
Sarkar, Tapomoy Guha
2009-01-01
Weak gravitational lensing of the CMBR manifests as a secondary anisotropy in the temperature maps. The effect, quantified through the shear and convergence fields imprint the underlying large scale structure (LSS), geometry and evolution history of the Universe. It is hence perceived to be an important observational probe of cosmology. De-lensing the CMBR temperature maps is also crucial for detecting the gravitational wave generated B-modes. Future observations of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI) distribution hold the potential of probing the LSS over a large redshift range. We have investigated the correlation between post-reionization HI signal and weak lensing convergence field. Assuming that the HI follows the dark matter distribution, the cross-correlation angular power spectrum at a multipole \\ell is found to be proportional to the cold dark matter power spectrum evaluated at \\ell/r, where r denotes the comoving distance to the redshift where the HI is located. Th...
Liu, W J; Ding, M D; Fang, C
2008-01-01
The direct current (DC) electric field near the reconnection region has been proposed as an effective mechanism to accelerate protons and electrons in solar flares. A power-law energy spectrum was generally claimed in the simulations of electron acceleration by the reconnection electric field. However, in most of the literature, the electric and magnetic fields were chosen independently. In this paper, we perform test particle simulations of electron acceleration in reconnecting magnetic field, where both the electric and magnetic fields are adopted from numerical simulations of the MHD equations. It is found that the accelerated electrons present a truncated power-law energy spectrum with an exponential tail at high energies, which is analogous to the case of diffusive shock acceleration. The influences of the reconnection parameters on the spectral feature are also investigated, such as the longitudinal and transverse components of the magnetic field and the size of the current sheet. It is suggested that t...
Peaks and Troughs in Helioseismology The Power Spectrum of Solar Oscillations
Rosenthal, C S
1998-01-01
I present a matched-wave asymptotic analysis of the driving of solar oscillations by a general localised source. The analysis provides a simple mathematical description of the asymmetric peaks in the power spectrum in terms of the relative locations of eigenmodes and troughs in the spectral response. It is suggested that the difference in measured phase function between the modes and the troughs in the spectrum will provide a key diagnostic of the source of the oscillations. I also suggest a form for the asymmetric line profiles to be used in the fitting of solar power spectra. Finally I present a comparison between the numerical and asymptotic descriptions of the oscillations. The numerical results bear out the qualitative features suggested by the asymptotic analysis but suggest that numerical calculations of the locations of the troughs will be necessary for a quantitative comparison with the observations.
Imprint of inhomogeneous and anisotropic primordial power spectrum on CMB polarization
Kothari, Rahul; Ghosh, Shamik; Rath, Pranati K.; Kashyap, Gopal; Jain, Pankaj
2016-08-01
We consider an inhomogeneous model and independently an anisotropic model of primordial power spectrum in order to describe the observed hemispherical anisotropy in cosmic microwave background radiation (CMBR). This anisotropy can be parametrized in terms of the dipole modulation model of the temperature field. Both the models lead to correlations between spherical harmonic coefficients corresponding to multipoles, l and l ± 1. We obtain the model parameters by making a fit to TT correlations in CMBR data. Using these parameters we predict the signature of our models for correlations among different multipoles for the case of the TE and EE modes. These predictions can be used to test whether the observed hemispherical anisotropy can be correctly described in terms of a primordial power spectrum. Furthermore these may also allow us to distinguish between an inhomogeneous and an anisotropic model.
The Nonlinear cosmological matter power spectrum with massive neutrinos. 1. The Halo model
Energy Technology Data Exchange (ETDEWEB)
Abazajian, Kevork; /Los Alamos; Switzer, Eric R.; /Princeton U.; Dodelson, Scott; /Fermilab /Chicago U., Astron. Astrophys. Ctr.; Heitmann, Katrin; Habib, Salman; /Los
2004-11-01
Measurements of the linear power spectrum of galaxies have placed tight constraints on neutrino masses. We extend the framework of the halo model of cosmological nonlinear matter clustering to include the effect of massive neutrino infall into cold dark matter (CDM) halos. The magnitude of the effect of neutrino clustering for three degenerate mass neutrinos with m{sub v{sub 1}} = 0.9 eV is of order {approx}1%, within the potential sensitivity of upcoming weak lensing surveys. In order to use these measurements to further constrain--or eventually detect--neutrino masses, accurate theoretical predictions of the nonlinear power spectrum in the presence of massive neutrinos will be needed, likely only possible through high-resolution multiple particle (neutrino, CDM and baryon) simulations.
The CMB temperature power spectrum from an improved analysis of the Archeops data
Tristram, M; Macias-Perez, J F; Ade, P; Amblard, A; Ansari, R; Aubourg, E; Benoît, A; Bernard, J P; Blanchard, A; Bock, J J; Bouchet, F R; Bourrachot, A; Camus, P; Cardoso, J F; Couchot, F; De Bernardis, P; Delabrouille, J; Désert, F X; Douspis, M; Dumoulin, L; Filliatre, P; Fosalba, P; Giard, M; Giraud-Héraud, Yannick; Gispert, R; Guglielmi, L; Hamilton, J C; Hanany, S; Henrot-Versillé, S; Kaplan, J; Lagache, G; Lange, A E; Madet, K; Maffei, B; Masi, S; Mayet, F; Nati, F; Perdereau, O; Plaszczynski, S; Piat, M; Ponthieu, N; Prunet, S; Renault, C; Rosset, C; Santos, D; Vibert, D; Yvon, D; Filliatre, Ph.
2004-01-01
We present improved results on the measurement of the angular power spectrum of the Cosmic Microwave Background (CMB) temperature anisotropies using the data from the last Archeops flight. This refined analysis is obtained by using the 6 most sensitive photometric pixels in the CMB bands centered at 143 and 217 GHz and 20% of the sky, mostly clear of foregrounds. Using two different cross-correlation methods, we obtain very similar results for the angular power spectrum. Consistency checks are performed to test the robustness of these results paying particular attention to the foreground contamination level which remains well below the statistical uncertainties. The multipole range from l=10 to l=700 is covered with 25 bins, confirming strong evidence for a plateau at large angular scales (the Sachs-Wolfe plateau) followed by two acoustic peaks centered around l=220 and l=550 respectively. These data provide an independent confirmation, obtained at different frequencies, of the WMAP first year results.
arXiv Neutrino masses and cosmology with Lyman-alpha forest power spectrum
Palanque-Delabrouille, Nathalie; Baur, Julien; Magneville, Christophe; Rossi, Graziano; Lesgourgues, Julien; Borde, Arnaud; Burtin, Etienne; LeGoff, Jean-Marc; Rich, James; Viel, Matteo; Weinberg, David
2015-01-01
We present constraints on neutrino masses, the primordial fluctuation spectrum from inflation, and other parameters of the $\\Lambda$CDM model, using the one-dimensional Ly$\\alpha$-forest power spectrum measured by Palanque-Delabrouille et al. (2013) from SDSS-III/BOSS, complemented by Planck 2015 cosmic microwave background (CMB) data and other cosmological probes. This paper improves on the previous analysis by Palanque-Delabrouille et al. (2015) by using a more powerful set of calibrating hydrodynamical simulations that reduces uncertainties associated with resolution and box size, by adopting a more flexible set of nuisance parameters for describing the evolution of the intergalactic medium, by including additional freedom to account for systematic uncertainties, and by using Planck 2015 constraints in place of Planck 2013. Fitting Ly$\\alpha$ data alone leads to cosmological parameters in excellent agreement with the values derived independently from CMB data, except for a weak tension on the scalar index ...
Generating non-Gaussian maps with a given power spectrum and bispectrum
Contaldi, C R; Contaldi, Carlo R.; Magueijo, Joao
2001-01-01
We propose two methods for generating non-Gaussian maps with fixed power spectrum and bispectrum. The first makes use of a recently proposed rigorous, non-perturbative, Bayesian framework for generating non-Gaussian distributions. The second uses a simple superposition of Gaussian distributions. The former is best suited for generating mildly non-Gaussian maps, and we discuss in detail the limitations of this method. The latter is better suited for the opposite situation, i.e. generating strongly non-Gaussian maps. The ensembles produced are isotropic and the power spectrum can be jointly fixed; however we cannot set to zero all other higher order cumulants (an unavoidable mathematical obstruction). We briefly quantify the leakage into higher order moments present in our method. We finally present an implementation of our code within the HEALPIX package
Bayesian joint estimation of non-Gaussianity and the power spectrum
Rocha, G; Hobson, M P; Lasenby, A; Rocha, Graca; Magueijo, Joao; Hobson, Mike; Lasenby, Anthony
2001-01-01
We propose a rigorous, non-perturbative, Bayesian framework which enables one jointly to test Gaussianity and estimate the power spectrum of CMB anisotropies. It makes use of the Hilbert space of an harmonic oscillator to set up an exact likelihood function, dependent on the power spectrum and on a set of parameters $\\alpha_i$, which are zero for Gaussian processes. The latter can be expressed as series of cumulants; indeed they perturbatively reduce to cumulants. However they have the advantage that their variation is essentially unconstrained. Any truncation(i.e.: finite set of $\\alpha_i$) therefore still produces a proper distribution - something which cannot be said of the only other such tool on offer, the Edgeworth expansion. We apply our method to Very Small Array (VSA) simulations based on signal Gaussianity, showing that our algorithm is indeed not biased.
Neutrino mass limits: Robust information from the power spectrum of galaxy surveys
Cuesta, Antonio J.; Niro, Viviana; Verde, Licia
2016-09-01
We present cosmological upper limits on the sum of active neutrino masses using large-scale power spectrum data from the WiggleZ Dark Energy Survey and from the Sloan Digital Sky Survey - Data Release 7 (SDSS-DR7) sample of Luminous Red Galaxies (LRG). Combining measurements on the Cosmic Microwave Background temperature and polarisation anisotropies by the Planck satellite together with WiggleZ power spectrum results in a neutrino mass bound of 0.37 eV at 95% C.L., while replacing WiggleZ by the SDSS-DR7 LRG power spectrum, the 95% C.L. bound on the sum of neutrino masses is 0.38 eV. Adding Baryon Acoustic Oscillation (BAO) distance scale measurements, the neutrino mass upper limits greatly improve, since BAO data break degeneracies in parameter space. Within a ΛCDM model, we find an upper limit of 0.13 eV (0.14 eV) at 95% C.L., when using SDSS-DR7 LRG (WiggleZ) together with BAO and Planck. The addition of BAO data makes the neutrino mass upper limit robust, showing only a weak dependence on the power spectrum used. We also quantify the dependence of neutrino mass limit reported here on the CMB lensing information. The tighter upper limit (0.13 eV) obtained with SDSS-DR7 LRG is very close to that recently obtained using Lyman-alpha clustering data, yet uses a completely different probe and redshift range, further supporting the robustness of the constraint. This constraint puts under some pressure the inverted mass hierarchy and favours the normal hierarchy.
High power density dc/dc converter: Component selection and design
Divan, Deepakraj M.
1989-01-01
Further work pertaining to design considerations for the new high power, high frequency dc/dc converters is discussed. The goal of the project is the development of high power, high power density dc/dc converters at power levels in the multi-kilowatt to megawatt range for aerospace applications. The prototype converter is rated for 50 kW at a switching frequency of 50 kHz, with an input voltage of 200 Vdc and an output of 2000 Vdc. The overall power density must be in the vicinity of 0.2 to 0.3 kg/kW.
A Ku-band high power density AlGaN/GaN HEMT monolithic power amplifier
Institute of Scientific and Technical Information of China (English)
Ge Qin; Chen Xiaojuan; Luo Weijun; Yuan Tingting; Pang Lei; Liu Xinyu
2011-01-01
A high power density monolithic power amplifier operated at Ku band is presented utilizing a 0.3 μm AlGaN/GaN HEMT production process on a 2-inch diameter semi-insulating (SI) 4H-SiC substrate by MOCVD.Over the 12-14 GHz frequency range,the single chip amplifier demonstrates a maximum power of 38 dBm (6.3 W),a peak power added efficiency (PAE) of 24.2% and linear gain of 6.4 to 7.5 dB under a 10% duty pulse conditionwhen operated at Vds =25 V and Vgs =-4 V.At these power levels,the amplifier exhibits a power density in excess of 5 W/mm.
Constraints on neutrino masses from Lyman-alpha forest power spectrum with BOSS and XQ-100
Yèche, Christophe; Palanque-Delabrouille, Nathalie; Baur, Julien; du Mas des Bourboux, Hélion
2017-06-01
We present constraints on masses of active and sterile neutrinos in the context of the ΛCDMν and ΛWDM models, respectively. We use the one-dimensional Lyα-forest power spectrum from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey (SDSS-III) measured by Palanque-Delabrouille et al. [1], and from the VLT/XSHOOTER legacy survey (XQ-100). In this paper, we present our own measurement of the publicly released XQ-100 quasar spectra, focusing in particular on an improved determination of the spectrograph resolution that allows us to push to smaller scales than the public release and reach k-modes of 0.070 s km-1. We compare the obtained 1D Lyα flux power spectrum to the one measured by Irsic et al. [2] to k-modes of 0.057 s km-1. Fitting Lyα data alone leads to cosmological parameters in excellent agreement with the values derived independently from Planck 2015 Cosmic Microwave Background (CMB) data. Combining BOSS and XQ-100 Lyα power spectra, we constrain the sum of neutrino masses to ∑ mν sources of systematic uncertainties. With the addition of CMB data, this bound is tightened to ∑ mν right-handed neutrinos. Combining the 1D Lyα-forest power spectrum measured by BOSS and XQ-100, we improve the two bounds to mX gtrsim 4.17 : keV and ms gtrsim 25.0 : keV (95% C.L.), slightly more constraining than what was achieved in Baur et al. 2015 [3] with BOSS data alone. The 3 σ bound shows a more significant improvement, increasing from mX gtrsim 2.74 : keV for BOSS alone to mX gtrsim 3.10 : keV for the combined BOSS+XQ-100 data set. Finally, we include in our analysis the first two redshift bins (z = 4.2 and z = 4.6) of the power spectrum measured by Viel et al. 2013 [4] with the high-resolution HIRES/MIKE spectrographs. The addition of HIRES/MIKE power spectrum allows us to further improve the two limits to mX gtrsim 4.65 : keV and ms gtrsim 28.8 : keV (95% C.L.).
Effects of motor programming on the power spectral density function of finger and wrist movements
Van Galen, G P; Van Doorn, R R; Schomaker, L R
1990-01-01
Power spectral density analysis was applied to the frequency content of the acceleration signal of pen movements in line drawing. The relative power in frequency bands between 1 and 32 Hz was measured as a function of motoric and anatomic task demands. Results showed a decrease of power at the lower
Spherical collapse, formation hysteresis and the deeply non-linear cosmological power spectrum
Mead, A. J.
2016-09-01
I examine differences in non-linear structure formation between cosmological models that share a z = 0 linear power spectrum in both shape and amplitude, but that differ via their growth history. N-body simulations of these models display an approximately identical large-scale-structure skeleton, but reveal deeply non-linear differences in the demographics and properties of haloes. I investigate to what extent the spherical-collapse model can help in understanding these differences, in both real and redshift space. I discuss how this is difficult to do if one attempts to identify haloes directly, because in that case one is subject to the vagaries of halo finding algorithms. However, I demonstrate that the halo model of structure formation provides an accurate non-linear response in the power spectrum, but only if results from spherical collapse that include formation hysteresis are properly incorporated. I comment on how this fact can be used to provide per cent level accurate matter power spectrum predictions for dark energy models for k ≤ 5 hMpc-1 by using the halo model as a correction to accurate ΛCDM simulations. In the appendix I provide some fitting functions for the linear-collapse threshold (δc) and virialized overdensity (Δv) that are valid for a wide range of dark energy models. I also make my spherical-collapse code available at https://github.com/alexander-mead/collapse.
The thermal Sunyaev Zel'dovich effect power spectrum in light of Planck
McCarthy, Ian G; Schaye, Joop; Holder, Gilbert P
2013-01-01
(Abridged) The amplitude of the thermal Sunyaev Zel'dovich effect (tSZ) power spectrum is extremely sensitive to the abundance of galaxy clusters and therefore to fundamental cosmological parameters that control their growth, such as sigma_8 and Omega_m. Here we explore the sensitivity of the tSZ power spectrum to important non-gravitational ('sub-grid') physics by employing the cosmo-OWLS suite of large-volume cosmological hydrodynamical simulations, run in both the Planck and WMAP7 best-fit cosmologies. On intermediate and small angular scales (ell > ~1000, or theta < ~10 arcmin), accessible with the South Pole Telescope and the Atacama Cosmology Telescope, the predicted tSZ power spectrum is highly model dependent, with AGN feedback having a particularly large effect. However, at large scales, observable with the Planck telescope, the effects of sub-grid physics are minor. Comparing the simulations with observations, we find a significant amplitude offset on all measured angular scales (including large ...
Cosmology Constraints from the Weak Lensing Peak Counts and the Power Spectrum in CFHTLenS
Liu, Jia; Haiman, Zoltan; Hui, Lam; Kratochvil, Jan M; May, Morgan
2014-01-01
Lensing peaks have been proposed as a useful statistic, containing cosmological information from non-Gaussianities that is inaccessible from traditional two-point statistics such as the power spectrum or two-point correlation functions. Here we examine constraints on cosmological parameters from weak lensing peak counts, using the publicly available data from the 154 deg^2 CFHTLenS survey. We utilize a new suite of ray-tracing N-body simulations on a grid of 91 cosmological models, covering broad ranges of the three parameters Omega_m, sigma_8, and w, and replicating the galaxy sky positions, redshifts, and shape noise in the CFHTLenS observations. We then build an emulator that interpolates the power spectrum and the peak counts to an accuracy of <= 5%, and compute the likelihood in the three-dimensional parameter space (Omega_m, sigma_8, w) from both observables. We find that constraints from peak counts are comparable to those from the power spectrum, and somewhat tighter when different smoothing scales...
Park, I H; McCall, W D; Chung, J W
2012-09-01
The relationship between temporomandibular joints (TMJ) osteoarthritis and masticatory muscle disorders is poorly understood. The data are sparse, the results are conflicting, and electromyographic (EMG) power spectrum analysis has not been used. The aims of this study were to compare the differences in EMG power spectrum during, and pressure pain thresholds (PPTs) before and after, sustained clenching in patients with unilateral TMJ osteoarthritis and healthy control subjects. Nineteen patients with unilateral TMJ osteoarthritis without masticatory muscle pain and 20 control subjects were evaluated. We measured EMG amplitudes at maximum voluntary contraction, median frequency from the EMG power spectrum during sustained clenching at 70% and PPTs before and after the clenching in both temporalis and masseter muscles. There were no significant differences in PPT decrease between muscles or between groups during sustained clenching. There were no significant differences in maximum voluntary contraction EMG activity ratios of affected to unaffected sides between groups, or of masseter to temporalis muscles between affected and unaffected side of patients with TMJ osteoarthritis. Median frequencies decreased from the beginning to the end of the sustained clench, and the interaction between group and clench was significant: the median frequency decrease was larger in the osteoarthritis group. Our results suggested that masticatory muscles of patients with unilateral TMJ osteoarthritis are more easily fatigued during sustained clenching than normal subjects. © 2012 Blackwell Publishing Ltd.
Neutrino mass limits: robust information from the power spectrum of galaxy surveys
Cuesta, Antonio J; Verde, Licia
2015-01-01
We present cosmological upper limits on the sum of active neutrino masses using large-scale power spectrum data from the WiggleZ Dark Energy Survey and from the Sloan Digital Sky Survey - Data Release 7 (SDSS-DR7) sample of Luminous Red Galaxies (LRG). Combining measurements on the Cosmic Microwave Background temperature and polarisation anisotropies by the Planck satellite together with WiggleZ power spectrum results in a neutrino mass bound of 0.43 eV at 95% C.L., while replacing WiggleZ by the SDSS-DR7 LRG power spectrum, the 95% C.L. bound on the sum of neutrino masses improves to 0.17 eV. Adding Baryon Acoustic Oscillation (BAO) distance scale measurements, the neutrino mass upper limits greatly improve, since BAO data break degeneracies in parameter space. Within a $\\Lambda$CDM model, we find an upper limit of 0.11 eV (0.15 eV) at 95% C.L., when using SDSS-DR7 LRG (WiggleZ) together with BAO and Planck. The addition of BAO data makes the neutrino mass upper limit robust, showing only a weak dependence o...
An effective field theory during inflation II: stochastic dynamics and power spectrum suppression
Boyanovsky, D
2015-01-01
We obtain the non-equilibrium effective action of an inflaton like scalar field --the system-- by tracing over sub Hubble degrees of freedom of ``environmental'' light scalar fields. The effective action is stochastic leading to effective Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and stochastic noise correlators that obey a de Sitter space-time analog of a fluctuation dissipation relation. We solve the Langevin equation implementing a dynamical renormalization group resummation of the leading secular terms and obtain the corrections to the power spectrum of super Hubble fluctuations of the inflaton field, $\\mathcal{P}(k;\\eta) = \\mathcal{P}_0(k)\\,e^{-\\gamma(k;\\eta)}$ where $\\mathcal{P}_0(k)$ is the nearly scale invariant power spectrum in absence of coupling. $\\gamma(k;\\eta)>0$ describes the suppression of the power spectrum, it features Sudakov-type double logarithms and entails violations of scale invariance. We also obtain the effective action...
Detecting the 21cm Forest in the 21 cm Power Spectrum
Ewall-Wice, Aaron; Mesinger, Andrei; Hewitt, Jacqueline
2013-01-01
Measurements of the 21 cm brightness temperature at high redshift are expected to yield tremendous insight into the nature of the first stars and black holes. A first generation of experiments is already underway, seeking a first detection. The brightness temperature fluctuations to be measured, also contain absorption features in the spectra of high redshift radio sources, the 21 cm forest. We describe a new technique for constraining the radio loud population of active galactic nuclei at high redshift by measuring the imprint of the 21 cm forest on the 21 cm power spectrum. We analytically relate the 21 cm forest power spectrum to the optical depth power spectrum and the radio loud luminosity function. Using semi-numeric simulations of the intergalactic medium and a semi-empirical source population, we show that the 21 cm forest dominates a distinctive region of k-space, $k \\gtrsim 0.5 \\Mpci$, allowing for the simultaneous determination of the intergalactic medium's thermal properties and the radio loud pop...
Spherical collapse, formation hysteresis and the deeply non-linear cosmological power spectrum
Mead, Alexander
2016-01-01
I examine differences in non-linear structure formation between cosmological models that share a $z=0$ linear power spectrum in both shape and amplitude, but that differ via their growth history. $N$-body simulations of these models display an approximately identical large-scale-structure skeleton, but reveal deeply non-linear differences in the demographics and properties of haloes. I investigate to what extent the spherical-collapse model can help in understanding these differences, in both real and redshift space. I discuss how this is difficult to do if one attempts to identify haloes directly, because in that case one is subject to the vagaries of halo finding algorithms. However, I demonstrate that the halo model of structure formation provides an accurate non-linear response in the power spectrum, but only if results from spherical collapse that include formation hysteresis are properly incorporated. I comment on how this fact can be used to provide per cent level accurate matter power spectrum predict...
Spherical collapse, formation hysteresis and the deeply non-linear cosmological power spectrum
Mead, A. J.
2017-01-01
I examine differences in non-linear structure formation between cosmological models that share a z = 0 linear power spectrum in both shape and amplitude, but that differ via their growth history. N-body simulations of these models display an approximately identical large-scale-structure skeleton, but reveal deeply non-linear differences in the demographics and properties of haloes. I investigate to what extent the spherical-collapse model can help in understanding these differences, in both real and redshift space. I discuss how this is difficult to do if one attempts to identify haloes directly, because in that case one is subject to the vagaries of halo-finding algorithms. However, I demonstrate that the halo model of structure formation provides an accurate non-linear response in the power spectrum, but only if results from spherical collapse that include formation hysteresis are properly incorporated. I comment on how this fact can be used to provide per cent level accurate matter power-spectrum predictions for dark energy models for k ≤ 5 h Mpc-1 by using the halo model as a correction to accurate ΛCDM simulations. In the Appendix, I provide some fitting functions for the linear-collapse threshold (δc) and virialized overdensity (Δv) that are valid for a wide range of dark energy models. I also make my spherical-collapse code available at https://github.com/alexander-mead/collapse.
Power spectrum sensitivity of raster-scanned CMB experiments in the presence of 1/f noise
Crawford, Tom
2007-09-01
We investigate the effects of 1/f noise on the ability of a particular class of cosmic microwave background experiments to measure the angular power spectrum of temperature anisotropy. We concentrate on experiments that operate primarily in raster-scan mode and develop formalism that allows us to calculate analytically the effect of 1/f noise on power-spectrum sensitivity for this class of experiments and determine the benefits of raster-scanning at different angles relative to the sky field versus scanning at only a single angle (cross-linking versus not cross-linking). We find that the sensitivity of such experiments in the presence of 1/f noise is not significantly degraded at moderate spatial scales (ℓ˜100) for reasonable values of scan speed and 1/f knee. We further find that the difference between cross-linked and non-cross-linked experiments is small in all cases and that the non-cross-linked experiments are preferred from a raw sensitivity standpoint in the noise-dominated regime—i.e., in experiments in which the instrument noise is greater than the sample variance of the target power spectrum at the scales of interest. This analysis does not take into account systematic effects.
Constraining high-redshift X-ray sources with next generation 21-cm power spectrum measurements
Ewall-Wice, Aaron; Hewitt, Jacqueline; Mesinger, Andrei; Dillon, Joshua S.; Liu, Adrian; Pober, Jonathan
2016-05-01
We use the Fisher matrix formalism and seminumerical simulations to derive quantitative predictions of the constraints that power spectrum measurements on next-generation interferometers, such as the Hydrogen Epoch of Reionization Array (HERA) and the Square Kilometre Array (SKA), will place on the characteristics of the X-ray sources that heated the high-redshift intergalactic medium. Incorporating observations between z = 5 and 25, we find that the proposed 331 element HERA and SKA phase 1 will be capable of placing ≲ 10 per cent constraints on the spectral properties of these first X-ray sources, even if one is unable to perform measurements within the foreground contaminated `wedge' or the FM band. When accounting for the enhancement in power spectrum amplitude from spin temperature fluctuations, we find that the observable signatures of reionization extend well beyond the peak in the power spectrum usually associated with it. We also find that lower redshift degeneracies between the signatures of heating and reionization physics lead to errors on reionization parameters that are significantly greater than previously predicted. Observations over the heating epoch are able to break these degeneracies and improve our constraints considerably. For these two reasons, 21-cm observations during the heating epoch significantly enhance our understanding of reionization as well.
Liu, Jia; Sherwin, Blake D; Petri, Andrea; Böhm, Vanessa; Haiman, Zoltán
2016-01-01
Unprecedentedly precise cosmic microwave background (CMB) data are expected from ongoing and near-future CMB Stage-III and IV surveys, which will yield reconstructed CMB lensing maps with effective resolution approaching several arcminutes. The small-scale CMB lensing fluctuations receive non-negligible contributions from nonlinear structure in the late-time density field. These fluctuations are not fully characterized by traditional two-point statistics, such as the power spectrum. Here, we use $N$-body ray-tracing simulations of CMB lensing maps to examine two higher-order statistics: the lensing convergence one-point probability distribution function (PDF) and peak counts. We show that these statistics contain significant information not captured by the two-point function, and provide specific forecasts for the ongoing Stage-III Advanced Atacama Cosmology Telescope (AdvACT) experiment. Considering only the temperature-based reconstruction estimator, we forecast 30$\\sigma$ (PDF) and 10$\\sigma$ (peaks) detec...
Achievable rate of spectrum sharing cognitive radio systems over fading channels at low-power regime
Sboui, Lokman
2014-11-01
We study the achievable rate of cognitive radio (CR) spectrum sharing systems at the low-power regime for general fading channels and then for Nakagami fading. We formally define the low-power regime and present the corresponding closed-form expressions of the achievable rate lower bound under various types of interference and/or power constraints, depending on the available channel state information of the cross link (CL) between the secondary-user transmitter and the primary-user receiver. We explicitly characterize two regimes where either the interference constraint or the power constraint dictates the optimal power profile. Our framework also highlights the effects of different fading parameters on the secondary link (SL) ergodic achievable rate. We also study more realistic scenarios when there is either 1-bit quantized channel feedback from the CL alone or 2-bit feedback from both the CL and the SL and propose simple power control schemes and show that these schemes achieve the previously achieved rate at the low-power regime. Interestingly, we show that the low-power regime analysis provides a specific insight into the maximum achievable rate behavior of CR that has not been reported by previous studies.
Hannah, I G; Reid, H A S
2012-01-01
To demonstrate the effect of turbulent background density fluctuations on flare accelerated electron transport in the solar corona. Using the quasi-linear approximation, we numerically simulate the propagation of a beam of accelerated electrons from the solar corona to chromosphere, including the self-consistent response of the inhomogeneous background plasma in the form of Langmuir waves. We calculate the X-ray spectrum from these simulations using the bremsstrahlung cross-section and fit the footpoint spectrum using the collisional "thick-target" model, a standard approach adopted in observational studies. We find that the interaction of the Langmuir waves with the background electron density gradient shifts the waves to higher phase velocity where they then resonate with higher velocity electrons. The consequence is that some of the electrons are shifted to higher energies, producing more high energy X-rays than expected in the cases where the density inhomogeneity is not considered. We find that the level...
Power spectral density and scaling exponent of high frequency global solar radiation sequences
Calif, Rudy; Schmitt, François G.; Huang, Yongxiang
2013-04-01
invariance: Iq(f) ~ f-?(q) , ?(q) is the scaling exponent. This allows to characterize the scaling behavior of a process: fractal or multifractal with intermittent properties. For q = 2, the Hilbert spectrum is defined. In this work, The data are collected at the University site of Guadeloupe, an island in the West Indies, located at 16°15 N latitude 60°30 W longitude. Our measurements sampled at 1 Hz were performed during one year period. The analyzed data present a power spectral density E(f) displaying a power law of the form E(f) ~ f-β with 1.6 ˜ β ˜ 2.2 for frequencies f ˜ 0.1 Hz, corresponding to time scales T × 10 s. Furthermore, global solar radiation data possesses multifractal properties. For comparison, other multifractal analysis techniques such as structure functions, MDFA, wavelet leaders are also used. This preliminary work set the basis for further investigation dedicated to simulate and forecast a sequence of solar energy fluctuation under different meteorological conditions, in the multifractal framework.
Feedback control of plasma density and heating power for steady state operation in LHD
Energy Technology Data Exchange (ETDEWEB)
Kamio, Shuji, E-mail: kamio@nifs.ac.jp; Kasahara, Hiroshi; Seki, Tetsuo; Saito, Kenji; Seki, Ryosuke; Nomura, Goro; Mutoh, Takashi
2015-12-15
Highlights: • We upgraded a control system for steady state operation in LHD. • This system contains gas fueling system and ICRF power control system. • Automatic power boost system is also attached for stable operation. • As a result, we achieved the long pulse up to 48 min in the electron density of more than 1 × 10{sup 19} m{sup −3}. - Abstract: For steady state operation, the feedback control of plasma density and heating power system was developed in the Large Helical Device (LHD). In order to achieve a record of the long pulse discharge, stable plasma density and heating power are needed. This system contains the radio frequency (RF) heating power control, interlocks, gas fueling, automatic RF phase control, ion cyclotron range of frequency (ICRF) antenna position control, and graphical user interface (GUI). Using the density control system, the electron density was controlled to the target density and using the RF heating power control system, the RF power injection could be stable. As a result of using this system, we achieved the long pulse up to 48 min in the electron density of more than 1 × 10{sup 19} m{sup −3}. Further, the ICRF hardware experienced no critical accidents during the 17th LHD experiment campaign in 2013.
Zhuravleva, I; Schekochihin, A A; Lau, E T; Nagai, D; Gaspari, M; Allen, S W; Nelson, K; Parrish, I J
2014-01-01
We address the problem of evaluating the power spectrum of the velocity field of the ICM using only information on the plasma density fluctuations, which can be measured today by Chandra and XMM-Newton observatories. We argue that for relaxed clusters there is a linear relation between the rms density and velocity fluctuations across a range of scales, from the largest ones, where motions are dominated by buoyancy, down to small, turbulent scales: $(\\delta\\rho_k/\\rho)^2 = \\eta_1^2 (V_{1,k}/c_s)^2$, where $\\delta\\rho_k/\\rho$ is the spectral amplitude of the density perturbations at wave number $k$, $V_{1,k}^2=V_k^2/3$ is the mean square component of the velocity field, $c_s$ is the sound speed, and $\\eta_1$ is a dimensionless constant of order unity. Using cosmological simulations of relaxed galaxy clusters, we calibrate this relation and find $\\eta_1\\approx 1 \\pm 0.3$. We argue that this value is set at large scales by buoyancy physics, while at small scales the density and velocity power spectra are proporti...
Influence of Mobile Users' Density Distribution on the CDMA Base Station Power
Lebl, Aleksandar; Mitić, Dragan; Popović, Miroslav; Markov, Žarko; Mileusnić, Mladen; Matić, Vladimir
2016-12-01
In this paper we analyze the influence of users' density distribution in one cell of CDMA mobile network (ie adjusted power control on the forward link) on base station emission power. This influence is analyzed for different circles radii around base station within which same emission power is generated for all mobile users, and for different values of propagation loss coefficient. It is proved that emission power in this cell must be increased comparing to the similar cell, which uses complete power control. The power increase is greater when greater number of users are situated near base station, and for greater values of propagation loss coefficient. The results are presented, illustrated by numerical examples and verified by simulation for three users' density distributions: uniform, decreasing and increasing density from the base station to the cell rim. The simulation process, which is based on random traffic process, is presented briefly.
Hurier, G.; Lacasa, F.
2017-08-01
The thermal Sunyaev-Zel'dovich (tSZ) effect is a powerful probe of the evolution of structures in the universe, and is thus highly sensitive to cosmological parameters σ8 and Ωm, though its power is hampered by the current uncertainties on the cluster mass calibration. In this analysis we revisit constraints on these cosmological parameters as well as the hydrostatic mass bias, by performing (i) a robust estimation of the tSZ power-spectrum, (ii) a complete modeling and analysis of the tSZ bispectrum, and (iii) a combined analysis of galaxy clusters number count, tSZ power spectrum, and tSZ bispectrum. From this analysis, we derive as final constraints σ8 = 0.79 ± 0.02, Ωm = 0.29 ± 0.02, and (1-b) = 0.71 ± 0.07. These results favor a high value for the hydrostatic mass bias compared to numerical simulations and weak-lensing based estimations. They are furthermore consistent with both previous tSZ analyses, CMB derived cosmological parameters, and ancillary estimations of the hydrostatic mass bias.
The 2-loop matter power spectrum and the IR-safe integrand
Energy Technology Data Exchange (ETDEWEB)
Carrasco, John Joseph M.; Foreman, Simon; Green, Daniel; Senatore, Leonardo, E-mail: jjmc@stanford.edu, E-mail: sfore@stanford.edu, E-mail: drgreen@stanford.edu, E-mail: senatore@stanford.edu [Stanford Institute for Theoretical Physics and Department of Physics, Stanford University, Stanford, CA 94306 (United States)
2014-07-01
Large scale structure surveys are likely the next leading probe of cosmological information. It is therefore crucial to reliably predict their observables. The Effective Field Theory of Large Scale Structures (EFTofLSS) provides a manifestly convergent perturbation theory for the weakly non-linear regime, where dark matter correlation functions are computed in an expansion of the wavenumber k over the wavenumber associated to the non-linear scale k{sub NL}. To push the predictions to higher wavenumbers, it is necessary to compute the 2-loop matter power spectrum. For equal-time correlators, exactly as with standard perturturbation theory, there are IR divergences present in each diagram that cancel completely in the final result. We develop a method by which all 2-loop diagrams are computed as one integral, with an integrand that is manifestly free of any IR divergences. This allows us to compute the 2-loop power spectra in a reliable way that is much less numerically challenging than standard techniques. We apply our method to scaling universes where the linear power spectrum is a single power law of k, and where IR divergences can particularly easily interfere with accurate evaluation of loop corrections if not handled carefully. We show that our results are independent of IR cutoff and, after renormalization, of the UV cutoff, and comment how the method presented here naturally generalizes to higher loops.
Institute of Scientific and Technical Information of China (English)
Han Li-Bo; Cao Li; Wu Da-Jin
2004-01-01
By using the linear approximation method, the output power spectrum is calculated for a single-mode laser driven by coloured pump and quantum noises with coloured correlation. We have observed that the configuration of the output power spectrum is complicated: that is, it can be of single peak, two peaks or three peaks. The configurations of the power spectrum can be transformed from one into another by changing the cross-correlation time, the cross-correlation coefficient between the two noises, and pump noise intensity.
Wojtkiewicz, S.; Liebert, A.; Rix, H.; Maniewski, R.
2011-12-01
In classical laser Doppler (LD) perfusion measurements, zeroth- and first-order moments of the power spectral density of the LD signal are utilized for the calculation of a signal corresponding to the concentration, speed and flow of red blood cells (RBCs). We have analysed the nonlinearities of the moments in relation to RBC speed distributions, parameters of filters utilized in LD instruments and the signal-to-noise ratio. We have developed a new method for fast simulation of the spectrum of the LD signal. The method is based on a superposition of analytically calculated Doppler shift probability distributions derived for the assumed light scattering phase function. We have validated the method by a comparison of the analytically calculated spectra with results of Monte Carlo (MC) simulations. For the semi-infinite, homogeneous medium and the single Doppler scattering regime, the analytical calculation describes LD spectra with the same accuracy as the MC simulation. The method allows for simulating the LD signal in time domain and furthermore analysing the index of perfusion for the assumed wavelength of the light, optical properties of the tissue and concentration of RBCs. Fast simulations of the LD signal in time domain and its frequency spectrum can be utilized in applications where knowledge of the LD photocurrent is required, e.g. in the development of detectors for tissue microperfusion monitoring or in measurements of the LD autocorrelation function for perfusion measurements. The presented fast method for LD spectra calculation can be used as a tool for evaluation of signal processing algorithms used in the LD method and/or for the development of new algorithms of the LD flowmetry and imaging. We analysed LD spectra obtained by analytical calculations using a classical algorithm applied in classical LD perfusion measurements. We observed nonlinearity of the first moment M1 for low and high speeds of particles (v 10 mm s-1). It was also noted that the
RegPT: Direct and fast calculation of regularized cosmological power spectrum at two-loop order
Taruya, Atsushi; Nishimichi, Takahiro; Codis, Sandrine
2012-01-01
We present a specific prescription for the calculation of cosmological power spectra, exploited here at two-loop order in perturbation theory (PT), based on the multi-point propagator expansion. In this approach power spectra are constructed from the regularized expressions of the propagators that reproduce both the resummed behavior in the high-k limit and the standard PT results at low-k. With the help of N-body simulations, we show that such a construction gives robust and accurate predictions for both the density power spectrum and the correlation function at percent-level in the weakly non-linear regime. We then present an algorithm that allows accelerated evaluations of all the required diagrams by reducing the computational tasks to one-dimensional integrals. This is achieved by means of pre-computed kernel sets defined for appropriately chosen fiducial models. The computational time for two-loop results is then reduced from a few minutes, with the direct method, to a few seconds with the fast one. The...
Is there a quantum gravity effect on the cosmic microwave background power spectrum?
Bini, Donato
2015-01-01
An assessment is made of recent attempts to evaluate how quantum gravity may affect the anisotropy spectrum of the cosmic microwave background. A perturbative scheme for the solution of the Wheeler-DeWitt equation has been found to allow for enhancement of power at large scales, whereas the alternative predicts a suppression of power at large scales. Both effects are corrections which, although conceptually interesting, turn out to be too small to be detected. Another scheme relies upon a Born-Oppenheimer analysis: by using a perturbative approach to the nonlinear ordinary differential equation obeyed by the two-point function for scalar fluctuations, a new family of power spectra have been obtained and studied by the authors.
Energy Technology Data Exchange (ETDEWEB)
Chien, C; Elgorriaga, I; McConaghy, C
2001-07-03
Emerging CMOS and MEMS technologies enable the implementation of a large number of wireless distributed microsensors that can be easily and rapidly deployed to form highly redundant, self-configuring, and ad hoc sensor networks. To facilitate ease of deployment, these sensors should operate on battery for extended periods of time. A particular challenge in maintaining extended battery lifetime lies in achieving communications with low power. This paper presents a direct-sequence spread-spectrum modem architecture that provides robust communications for wireless sensor networks while dissipating very low power. The modem architecture has been verified in an FPGA implementation that dissipates only 33 mW for both transmission and reception. The implementation can be easily mapped to an ASIC technology, with an estimated power performance of less than 1 mW.
Benkhelifa, Fatma
2016-07-26
In this paper, we consider the simultaneous wireless information and power transfer for the spectrum sharing (SS) in cognitive radio (CR) systems with a multi-antenna energy harvesting (EH) primary receiver (PR). The PR uses the antenna switching (AS) technique that assigns a subset of the PR\\'s antennas to harvest the energy from the radio frequency (RF) signals sent by the secondary transmitter (ST), and assigns the rest of the PR\\'s antennas to decode the information data. In this context, the primary network allows the secondary network to use the spectrum as long as the interference induced by the secondary transmitter (ST)\\'s signals is beneficial for the energy harvesting process at the PR side. The objective of this work is to show that the spectrum sharing is beneficial for both the SR and PR sides and leads to a win-win situation. To illustrate the incentive of the spectrum sharing cognitive system, we evaluate the mutual outage probability (MOP) introduced in [1] which declares an outage event if the PR or the secondary receiver (SR) is in an outage. Through the simulation results, we show that the performance of our system in terms of the MOP is always better than the performance of the system in the absence of ST and improves as the ST-PR interference increases. © 2016 IEEE.
Perturbation theory, effective field theory, and oscillations in the power spectrum
Vlah, Zvonimir; Seljak, Uroš; Yat Chu, Man; Feng, Yu
2016-03-01
We explore the relationship between the nonlinear matter power spectrum and the various Lagrangian and Standard Perturbation Theories (LPT and SPT). We first look at it in the context of one dimensional (1-d) dynamics, where 1LPT is exact at the perturbative level and one can exactly resum the SPT series into the 1LPT power spectrum. Shell crossings lead to non-perturbative effects, and the PT ignorance can be quantified in terms of their ratio, which is also the transfer function squared in the absence of stochasticity. At the order of PT we work, this parametrization is equivalent to the results of effective field theory (EFT), and can thus be expanded in terms of the same parameters. We find that its radius of convergence is larger than the SPT loop expansion. The same EFT parametrization applies to all SPT loop terms and if stochasticity can be ignored, to all N-point correlators. In 3-d, the LPT structure is considerably more complicated, and we find that LPT models with parametrization motivated by the EFT exhibit running with k and that SPT is generally a better choice. Since these transfer function expansions contain free parameters that change with cosmological model their usefulness for broadband power is unclear. For this reason we test the predictions of these models on baryonic acoustic oscillations (BAO) and other primordial oscillations, including string monodromy models, for which we ran a series of simulations with and without oscillations. Most models are successful in predicting oscillations beyond their corresponding PT versions, confirming the basic validity of the model. We show that if primordial oscillations are localized to a scale q, the wiggles in power spectrum are approximately suppressed as exp[-k2Σ2(q)/2], where Σ(q) is rms displacement of particles separated by q, which saturates on large scales, and decreases as q is reduced. No oscillatory features survive past k ~ 0.5h/Mpc at z = 0.
The influence of the type of contraction on the masseter muscle EMG power spectrum.
Nadeau, S; Bilodeau, M; Delisle, A; Chmielewski, W; Arsenault, A B; Gravel, D
1993-01-01
Different behaviours of the EMG power spectrum across increasing force levels have been reported for the masseter muscle. A factor that could explain these different behaviours may be the type of contraction used, as was recently shown for certain upper limb muscles(5). The purpose of this study was to compare, between two types of isometric contractions, the behaviour of EMG power spectrum statistics (median frequency (MF) and mean power frequency (MPF)) obtained across increasing force levels. Ten women exerted, while biting in the intercuspal position, three 5 s ramp contractions that increased linearly from 0 to 100% of the maximal voluntary contraction (MVC). They also completed three step contractions (constant EMG amplitude) at each of the following levels: 20, 40, 60 and 80% MVC. EMG signals from the masseter muscle were recorded with miniature surface electrodes. The RMS, as well as the MPF and MF of the power spectrum were calculated at 20, 40, 60 and 80% MVC for each type of contraction. As expected, the RMS values showed similar increases with increasing levels of effort for both types of contractions. Different behaviours for both MPF (contraction(∗)force interaction, ANOVA, P0.05) across increasing levels of effort were found between the two types of contraction. The use of step contractions gave rise to a decrease of both MPF and MF with increasing force, while the use of ramp contractions gave rise to an increase in both statistics up to at least 40% MVC followed by a decrease at higher force levels. These findings suggest that the type of contraction used does influence the behaviour of the spectral statistics across increasing force levels and that this could explain the differences obtained in previous studies for the masseter muscle. Copyright © 1993. Published by Elsevier Ltd.
Reconstruction of the primordial power spectrum of curvature perturbations using multiple data sets
DEFF Research Database (Denmark)
Hunt, Paul; Sarkar, Subir
2014-01-01
Detailed knowledge of the primordial power spectrum of curvature perturbations is essential both in order to elucidate the physical mechanism (`inflation') which generated it, and for estimating the cosmological parameters from observations of the cosmic microwave background and large-scale struc......Detailed knowledge of the primordial power spectrum of curvature perturbations is essential both in order to elucidate the physical mechanism (`inflation') which generated it, and for estimating the cosmological parameters from observations of the cosmic microwave background and large......-scale structure. Hence it ought to be extracted from such data in a model-independent manner, however this is difficult because relevant cosmological observables are given by a convolution of the primordial perturbations with some smoothing kernel which depends on both the assumed world model and the matter...... content of the universe. Moreover the deconvolution problem is ill-conditioned so a regularisation scheme must be employed to control error propagation. We demonstrate that `Tikhonov regularisation' can robustly reconstruct the primordial spectrum from multiple cosmological data sets, a significant...
Application of beam deconvolution technique to power spectrum estimation for CMB measurements
Keihänen, Elina; Kurki-Suonio, Hannu; Reinecke, Martin
2016-01-01
We present two novel methods for the estimation of the angular power spectrum of cosmic microwave background (CMB) anisotropies. We assume an absolute CMB experiment with arbitrary asymmetric beams and arbitrary sky coverage. The methods differ from earlier ones in that the power spectrum is estimated directly from time-ordered data, without first compressing the data into a sky map, and they take into account the effect of asymmetric beams. In particular, they correct the beam-induced leakage from temperature to polarization. The methods are applicable to a case where part of the sky has been masked out to remove foreground contamination, leaving a pure CMB signal, but incomplete sky coverage. The first method (DQML) is derived as the optimal quadratic estimator, which simultaneously yields an unbiased spectrum estimate, and minimizes its variance. We successfully apply it to multipoles up to $\\ell$=200. The second method is derived as an weak-signal approximation from the first one. It yields an unbiased es...
So You Think the Crab is Described by a Power-Law Spectrum
Weisskopf, Martin C.
2008-01-01
X-ray observations of the Crab Nebula and its pulsar have played a prominent role in the history of X-ray astronomy. Discoveries range from the detection of the X-ray Nebula and pulsar and the measurement of the Nebula-averaged X-ray polarization, to the observation of complex X-ray morphology, including jets emanating from the pulsar and the ring defining the shocked pulsar wind. The synchrotron origin of much of the radiation has been deduced by detailed studies across the electromagnetic spectrum, yet has fooled many X-ray astronomers into believing that the integrated spectrum from this system ought to be a power law. In many cases, this assumption has led observers to adjust the experiment response function(s) to guarantee such a result. We shall discuss why one should not observe a power-law spectrum, and present simulations using the latest available response matrices showing what should have been observed for a number of representative cases including the ROSAT IPC, XMM-Newton, and RXTE. We then discuss the implications, if any, for current calibrations.
Modelling the Autocovariance of the Power Spectrum of a Solar-Type Oscillator
Campante, T L; Chaplin, W J; Elsworth, Y P; Handberg, R; Hekker, S
2010-01-01
Asteroseismology is able to conduct studies on the interiors of solar-type stars from the analysis of stellar acoustic spectra. However, such an analysis process often has to rely upon subjective choices made throughout. A recurring problem is to determine whether a signal in the acoustic spectrum originates from a radial or a dipolar oscillation mode. In order to overcome this problem, we present a procedure for modelling and fitting the autocovariance of the power spectrum which can be used to obtain global seismic parameters of solar-type stars, doing so in an automated fashion without the need to make subjective choices. From the set of retrievable global seismic parameters we emphasize the mean small frequency separation and, depending on the intrinsic characteristics of the power spectrum, the mean rotational frequency splitting. Since this procedure is automated, it can serve as a useful tool in the analysis of the more than one thousand solar-type stars expected to be observed as part of the Kepler As...
High power density electrodes for Carbon supercapacitor applications
Energy Technology Data Exchange (ETDEWEB)
Portet, C.; Taberna, P.L.; Simon, P.; Flahaut, E.; Laberty-Robert, C. [CIRIMAT, UMR CNRS 5085, 118 Route de Narbonne 31062 Toulouse Cedex (France)
2005-07-25
This paper presents results obtained with 4 cm{sup 2} Carbon/Carbon supercapacitors cells in organic electrolyte. In the first approach, a surface treatment for Al current collector foil via the sol-gel route has been used in order to decrease the Al/active material interface resistance. Performances obtained with this original process are: a low equivalent series resistance (ESR) of 0.5 {omega} cm{sup 2} and a specific capacitance of 95 F g{sup -1} of activated carbon. Then, supercapacitors assembled with treated Al foil and active material containing activated carbon/carbon nanotubes (CNTs) with different compositions have been studied. Galvanostatic cycling measurements show that when CNTs content increases, both ESR and specific capacitance are decreased. Fifteen percent appears to be a good compromise between stored energy and delivered power with an ESR of 0.4 {omega} cm{sup 2} and a specific capacitance of 93 F g{sup -1} of carbonaceous active material. Finally, cells frequency behaviour has been characterized by Electrochemical Impedance Spectroscopy. The relaxation time constant of cells decreases when the CNTs content increases. For 15% of CNTs, the time constant is about 30% lower as compared to a cell using pure activated carbon-based electrodes leading to a higher delivered power. (author)
Nanomaterials Enabled High Energy and Power Density Li-ion Batteries Project
National Aeronautics and Space Administration — There is a need for high energy (~ 200 Wh/kg) and high power (> 500 W/kg) density rechargeable Li-ion batteries that are safe and reliable for several space and...
Characteristics of the Velocity Power Spectrum as a Function of Taylor Reynolds Number
Puga, Alejandro J.
An understanding of the wide range of scales present in a turbulent flow as well as the turbulence kinetic energy associated with those scales can provide significant insight into the modeling of such flows. Since turbulence is a stochastic process, statistical quantities such as mean, root mean square, correlations and spectra are used to identify and understand the evolution of turbulent flows. Time-resolved velocity measurements presented herein are obtained using hot-wire anemometry in nearly homogeneous, isotropic and moderately high Taylor Reynolds number, Rlambda , flow downstream of an active grid. Velocity power spectra presented herein are show that the slope, n, of the inertial subrange, where the inertial subrange is defined as the wavenumber range where the power spectrum scales as kappa--n, varies with R lambda as n = 1.69 -- 5.86 Rlambda--0.645. This variation in the slope of the inertial subrange is consistent with measurements presented by Mydlarski and Warhaft (1996) in an active grid flow and Saddoughi and Veeravalli (1994) in a turbulent boundary layer. The effectiveness of velocity power spectrum normalizations proposed by Kolmogorov (1963), Von Karman and Howarth (1938), and George (1992) are compared qualitatively and quantitatively. The effectiveness of these normalizations suggests how the turbulent scales make specific portions of the velocity spectrum self-similar. It is found that the relation between the large and small scales is also shown by the normalized dissipation rate, which is defined as the dissipation rate normalized by the ratio of the turbulence kinetic energy to the time scale of the large scale structure is shown to be a constant with respect to R lambda for Rlambda ≥ 450. A modified model of the one-dimensional velocity power spectrum is proposed that is based on a model proposed by Pope (2000), which has been demonstrated to model power spectra at high value of Rlambda where the slope of the inertial subrange is very
Distributed joint power and access control algorithm for secondary spectrum sharing
Li, Hongyan; Chen, Enqing; Fu, Hongliang
2010-08-01
Based on interference temperature model, the problem of efficient secondary spectrum sharing is formulated as a power optimization problem with some constraints at physical layer. These constraints and optimization objective limit a feasible power vector set which leads to the need of access control besides power control. In this paper, we consider the decentralized cognitive radio network scenario where short-term data service is required, and the problem of distributed joint power and access control is studied to maximize the total secondary system throughput, subject to Quality of Service (QoS) constraints from individual secondary users and interference temperature limit (ITL) from primary system. Firstly, a pricing-based game model was used to solve distributed power allocation optimization problem in both high and low signal to interference noise ratio (SINR) scenarios. Secondly, when not all the secondary links can be supported with their QoS requirement and ITL, a distributed joint power and access control algorithm was introduced to find the allowable links which results in maximum network throughput with all the constraints satisfied, and the convergence performance is tested by simulations.
Power Spectrum Analysis of Polarized Emission from the Canadian Galactic Plane Survey
Stutz, R A; Kothes, R; Landecker, T
2014-01-01
Angular power spectra are calculated and presented for the entirety of the Canadian Galactic Plane Survey polarization dataset at 1.4 GHz covering an area of 1060 deg$^2$. The data analyzed are a combination of data from the 100-m Effelsberg Telescope, the 26-m Telescope at the Dominion Radio Astrophysical Observatory, and the Synthesis Telescope at the Dominion Radio Astrophysical Observatory, allowing all scales to be sampled down to arcminute resolution. The resulting power spectra cover multipoles from $\\ell \\approx 60$ to $\\ell \\approx 10^4$ and display both a power-law component at low multipoles and a flattening at high multipoles from point sources. We fit the power spectrum with a model that accounts for these components and instrumental effects. The resulting power-law indices are found to have a mode of 2.3, similar to previous results. However, there are significant regional variations in the index, defying attempts to characterize the emission with a single value. The power-law index is found to ...
The Scale-invariant Power Spectrum of Primordial Curvature Perturbation in CSTB Cosmos
Li, Changhong
2014-01-01
We investigate the spectrum of cosmological perturbations in a bounce cosmos modeled by a scalar field coupled to the string tachyon field (CSTB cosmos). By explicit computation of its primordial spectral index we show the power spectrum of curvature perturbations, generated during the tachyon matter dominated contraction phase, to be nearly scale invariant. We propose a unified space of parameters for a systematic study of inflationary/bouncing cosmologies. We find that CSTB cosmos is dual--in Wands's sense--to the slow-roll inflation model as can be easily seen from this unified parameter space. Guaranteed by the dynamical attractor behavior of CSTB Cosmos, this scale invariance is free of the fine-tuning problem, in contrast to the slow-roll inflation model.
Reconstruction of the primordial power spectrum of curvature perturbations using multiple data sets
DEFF Research Database (Denmark)
Hunt, Paul; Sarkar, Subir
2014-01-01
Detailed knowledge of the primordial power spectrum of curvature perturbations is essential both in order to elucidate the physical mechanism (`inflation') which generated it, and for estimating the cosmological parameters from observations of the cosmic microwave background and large......-scale structure. Hence it ought to be extracted from such data in a model-independent manner, however this is difficult because relevant cosmological observables are given by a convolution of the primordial perturbations with some smoothing kernel which depends on both the assumed world model and the matter...... content of the universe. Moreover the deconvolution problem is ill-conditioned so a regularisation scheme must be employed to control error propagation. We demonstrate that `Tikhonov regularisation' can robustly reconstruct the primordial spectrum from multiple cosmological data sets, a significant...
Hazra, Milan
2016-01-01
Valuable dynamical and structural information about neat liquid DMSO at ambient conditions can be obtained through study of low frequency vibrations in the far infrared (FIR), that is, terahertz regime. For DMSO, collective excitations as well as single molecule stretches and bends have been measured by different kinds of experiments such as OHD-RIKES and terahertz spectroscopy. In the present work we investigate the intermolecular vibrational spectrum of DMSO through three different computational techniques namely (i) the far-infra red spectrum obtained through Fourier transform of total dipole moment auto time correlation function, (ii) from Fourier transform of the translational and angular velocity time autocorrelation functions and a (iii) quenched normal mode analysis of the parent liquid at 300K. The three spectrum, although exhibit differences among each other, reveal similar features which are in good, semi-quantitative, agreement with experimental results. Study of participation ratio of the density...
The spectral density function for the Laplacian on high tensor powers of a line bundle
2001-01-01
For a symplectic manifold with quantizing line bundle, a choice of almost complex structure determines a Laplacian acting on tensor powers of the bundle. For high tensor powers Guillemin-Uribe showed that there is a well-defined cluster of low-lying eigenvalues, whose distribution is described by a spectral density function. We give an explicit computation of the spectral density function, by constructing certain quasimodes on the associated principle bundle.
Design of Ultra-High-Power-Density Machine Optimized for Future Aircraft
Choi, Benjamin B.
2004-01-01
The NASA Glenn Research Center's Structural Mechanics and Dynamics Branch is developing a compact, nonpolluting, bearingless electric machine with electric power supplied by fuel cells for future "more-electric" aircraft with specific power in the projected range of 50 hp/lb, whereas conventional electric machines generate usually 0.2 hp/lb. The use of such electric drives for propulsive fans or propellers depends on the successful development of ultra-high-power-density machines. One possible candidate for such ultra-high-power-density machines, a round-rotor synchronous machine with an engineering current density as high as 20,000 A/sq cm, was selected to investigate how much torque and power can be produced.
Agarwal, Shankar; Feldman, Hume A; Lahav, Ofer; Thomas, Shaun A
2013-01-01
In this paper we introduce PkANN, a freely available software package for interpolating the non-linear matter power spectrum, constructed using Artificial Neural Networks (ANNs). Previously, using Halofit to calculate matter power spectrum, we demonstrated that ANNs can make extremely quick and accurate predictions of the power spectrum. Now, using a suite of 6380 N-body simulations spanning 580 cosmologies, we train ANNs to predict the power spectrum over the cosmological parameter space spanning $3\\sigma$ confidence level (CL) around the concordance cosmology. When presented with a set of cosmological parameters ($\\Omega_{\\rm m} h^2, \\Omega_{\\rm b} h^2, n_s, w, \\sigma_8, \\sum m_\
Periodic power spectrum with applications in detection of latent periodicities in DNA sequences.
Yin, Changchuan; Wang, Jiasong
2016-11-01
Periodic elements play important roles in genomic structures and functions, yet some complex periodic elements in genomes are difficult to detect by conventional methods such as digital signal processing and statistical analysis. We propose a periodic power spectrum (PPS) method for analyzing periodicities of DNA sequences. The PPS method employs periodic nucleotide distributions of DNA sequences and directly calculates power spectra at specific periodicities. The magnitude of a PPS reflects the strength of a signal on periodic positions. In comparison with Fourier transform, the PPS method avoids spectral leakage, and reduces background noise that appears high in Fourier power spectrum. Thus, the PPS method can effectively capture hidden periodicities in DNA sequences. Using a sliding window approach, the PPS method can precisely locate periodic regions in DNA sequences. We apply the PPS method for detection of hidden periodicities in different genome elements, including exons, microsatellite DNA sequences, and whole genomes. The results show that the PPS method can minimize the impact of spectral leakage and thus capture true hidden periodicities in genomes. In addition, performance tests indicate that the PPS method is more effective and efficient than a fast Fourier transform. The computational complexity of the PPS algorithm is [Formula: see text]. Therefore, the PPS method may have a broad range of applications in genomic analysis. The MATLAB programs for implementing the PPS method are available from MATLAB Central ( http://www.mathworks.com/matlabcentral/fileexchange/55298 ).
What is the optimal way to measure the galaxy power spectrum?
Smith, Robert E
2015-01-01
Measurements of the galaxy power spectrum contain a wealth of information about the Universe. Its optimal extraction is vital if we are to truly understand the micro-physical nature of dark matter and dark energy. In Smith & Marian (2015) we generalized the power spectrum methodology of Feldman et al. (1994) to take into account the key tenets of galaxy formation: galaxies form and reside exclusively in dark matter haloes; a given dark matter halo may host galaxies of various luminosities; galaxies inherit the large-scale bias associated with their host halo. In this paradigm we derived the optimal weighting and reconstruction scheme for maximizing the signal-to-noise on a given band power estimate. For a future all-sky flux-limited galaxy redshift survey of depth b_J ~22, we now demonstrate that the optimal weighting scheme does indeed provide improved S/N at the level of ~20% when compared to Feldman et al. (1994) and ~60% relative to Percival et al. (2003), for scales of order k~0.5 Mpc/h. Using a Fish...
Analytic model for the matter power spectrum, its covariance matrix, and baryonic effects
Mohammed, Irshad
2014-01-01
We develop a model for the matter power spectrum as the sum of quasi-linear Zeldovich approximation and even powers of $k$, i.e., $A_0 - A_2k^2 + A_4k^4 - ...$, compensated at low $k$. The model can predict the true power spectrum to a few percent accuracy up to $k \\sim 0.7\\ h \\rm{Mpc}^{-1}$, over a wide range of redshifts and models, including massive neutrino models. We write a simple form of the covariance matrix as a sum of Gaussian part and $A_0$ variance and we find that it reproduces well the simulations. We investigate the super-sample variance effect and show it induces a relation between the Zeldovich term and $A_0$ that differs from the amplitude change, allowing it to be modeled as an additional parameter that can be determined from the data. The $A_n$ coefficients contain information about cosmology, in particular the amplitude of fluctuations $\\sigma_8$. We explore their information content, showing that $A_0$ contains the bulk of amplitude information, scaling as $\\sigma_8^{3.9}$, which allows ...
Institute of Scientific and Technical Information of China (English)
ZHUANG You-Yi; ZHANG Yao-Ju
2009-01-01
A new design is presented to improve the magnetic recording density in all-optical magnetic storage.By using the high numerical lens with a high-pass angular spectrum filter, circularly polarized laser pulses are focused into the magneto-optic film with the perpendicular anisotropy.Magnetization of the film is induced by the inverse Faraday effect.As the obstructed angle of the filter increases the magnetic recording density increases evidently.The magnetization intensity and the sidelobe effect are also discussed.
The effects of high density on the X-ray spectrum reflected from accretion discs around black holes
García, Javier A.; Fabian, Andrew C.; Kallman, Timothy R.; Dauser, Thomas; Parker, Michael L.; McClintock, Jeffrey E.; Steiner, James F.; Wilms, Jörn
2016-10-01
Current models of the spectrum of X-rays reflected from accretion discs around black holes and other compact objects are commonly calculated assuming that the density of the disc atmosphere is constant within several Thomson depths from the irradiated surface. An important simplifying assumption of these models is that the ionization structure of the gas is completely specified by a single, fixed value of the ionization parameter ξ, which is the ratio of the incident flux to the gas density. The density is typically fixed at ne = 1015 cm-3. Motivated by observations, we consider higher densities in the calculation of the reflected spectrum. We show by computing model spectra for ne ≳ 1017 cm-3 that high-density effects significantly modify reflection spectra. The main effect is to boost the thermal continuum at energies ≲ 2 keV. We discuss the implications of these results for interpreting observations of both active galactic nuclei and black hole binaries. We also discuss the limitations of our models imposed by the quality of the atomic data currently available.
DOUBLE POWER LAWS IN THE EVENT-INTEGRATED SOLAR ENERGETIC PARTICLE SPECTRUM
Energy Technology Data Exchange (ETDEWEB)
Zhao, Lulu; Zhang, Ming; Rassoul, Hamid K., E-mail: lzhao@fit.edu [Physics and Space Sciences Department, Florida Institute of Technology, Melbourne, FL 32901 (United States)
2016-04-10
A double power law or a power law with exponential rollover at a few to tens of MeV nucleon{sup −1} of the event-integrated differential spectra has been reported in many solar energetic particle (SEP) events. The rollover energies per nucleon of different elements correlate with a particle's charge-to-mass ratio (Q/A). The probable causes are suggested as residing in shock finite lifetimes, shock finite sizes, shock geometry, and an adiabatic cooling effect. In this work, we conduct a numerical simulation to investigate a particle's transport process in the inner heliosphere. We solve the focused transport equation using a time-backward Markov stochastic approach. The convection, magnetic focusing, adiabatic cooling effect, and pitch-angle scattering are included. The effects that the interplanetary turbulence imposes on the shape of the resulting SEP spectra are examined. By assuming a pure power-law differential spectrum at the Sun, a perfect double-power-law feature with a break energy ranging from 10 to 120 MeV nucleon{sup −1} is obtained at 1 au. We found that the double power law of the differential energy spectrum is a robust result of SEP interplanetary propagation. It works for many assumptions of interplanetary turbulence spectra that give various forms of momentum dependence of a particle's mean free path. The different spectral shapes in low-energy and high-energy ends are not just a transition from the convection-dominated propagation to diffusion-dominated propagation.
Heating and Life Problem of High Power Density Induction Motor
Institute of Scientific and Technical Information of China (English)
李立毅; 崔淑梅; 宋立伟; 胡余生
2004-01-01
An induction motor with its speed modulated by frequency features wide transfer speed range, high systematic efficiency, simple structure and long life, and it therefore becomes one of the best driving motors used in electrical vehicles. The present research trend of it is high power, high speed, high efficiency and long life. How to meet the above requirements by using the electromagnetic design, structure design and heat design, becomes a matter that needs to be resolved now. In this paper, the characters of the motor in operation are analyzed, all kinds of factors that relate to life are laid out, its heating and loss are discussed and analyzed.The key reasons affecting the motor life are presented, and different characters of a high induction motor are compared with these of a general induction motor. A design idea is described, that is: we should consider how to improve the efficiency and reliability as well as how to reduce the heating by changing the electromagnet,structure, dissipation and operation of the motor. How to reduce its losses and to improve its dissipation has been presented in the paper.
Atlas Pulsed Power Facility for High Energy Density Physics Experiments
Energy Technology Data Exchange (ETDEWEB)
Miller, R.B.; Ballard, E.O.; Barr, G.W.; Bowman, D.W.; Chochrane, J.C.; Davis, H.A.; Elizondo, J.M.; Gribble, R.F.; Griego, J.R.; Hicks, R.D.; Hinckley, W.B.; Hosack, K.W.; Nielsen, K.E.; Parker, J.V.; Parsons, M.O.; Rickets, R.L.; Salazar, H.R.; Sanchez, P.G.; Scudder, D.W.; Shapiro, C.; Thompson, M.C.; Trainor, R.J.; Valdez, G.A.; Vigil, B.N.; Watt, R.G.; Wysock, F.J.
1999-06-07
The Atlas facility, now under construction at Los Alamos National Laboratory (LANL), will provide a unique capability for performing high-energy-density experiments in support of weapon-physics and basic-research programs. It is intended to be an international user facility, providing opportunities for researchers from national laboratories and academic institutions around the world. Emphasizing institutions around the world. Emphasizing hydrodynamic experiments, Atlas will provide the capability for achieving steady shock pressures exceeding 10-Mbar in a volume of several cubic centimeters. In addition, the kinetic energy associated with solid liner implosion velocities exceeding 12 km/s is sufficient to drive dense, hydrodynamic targets into the ionized regime, permitting the study of complex issues associated with strongly-coupled plasmas. The primary element of Atlas is a 23-MJ capacitor bank, comprised of 96 separate Marx generators housed in 12 separate oil-filled tanks, surrounding a central target chamber. Each tank will house two, independently-removable maintenance units, with each maintenance unit consisting of four Marx modules. Each Marx module has four capacitors that can each be charged to a maximum of 60 kilovolts. When railgap switches are triggered, the marx modules erect to a maximum of 240 kV. The parallel discharge of these 96 Marx modules will deliver a 30-MA current pulse with a 4-5-{micro}s risetime to a cylindrical, imploding liner via 24 vertical, tri-plate, oil-insulated transmission lines. An experimental program for testing and certifying all Marx and transmission line components has been completed. A complete maintenance module and its associated transmission line (the First Article) are now under construction and testing. The current Atlas schedule calls for construction of the machine to be complete by August, 2000. Acceptance testing is scheduled to begin in November, 2000, leading to initial operations in January, 2001.
PkANN I: Non-Linear Matter Power Spectrum Estimation through Artificial Neural Networks
Agarwal, Shankar; Feldman, Hume A; Lahav, Ofer; Thomas, Shaun A
2012-01-01
We investigate a new approach to confront small-scale non-linearities in the power spectrum of matter fluctuations. This ever-present and pernicious uncertainty is often the Achilles' heel in cosmological studies and must be reduced if we are to see the advent of precision cosmology in the late-time Universe. We show that an optimally trained Artificial Neural Network (ANN), when presented with a set of cosmological parameters ($\\Omega_{\\rm m} h^2, \\Omega_{\\rm b} h^2, n_s, w_0, \\sigma_8, \\sum m_\
Blind Carrier Frequency Offset Estimation via Power Spectrum Analysis in MIMO OFDM Systems
Institute of Scientific and Technical Information of China (English)
WU Lu; ZHANG Xianda
2009-01-01
As a generalization of orthogonal frequency-division multiplexing (OFDM) systems,multi-input multi-output (MIMO) OFDM systems are very sensitive to carrier frequency offset (CFO).This paper proposes a blind CFO estimation method based on power spectrum analysis,which has high bandwidth efficiency and is much less complex.This method can be used to estimate the residual CFO,which is less than half of the subcarrier spacing.The method uses a cosine cost function to get a closed-form CFO estimate.Simulation results illustrate that the method is effective for MIMO OFDM systems.
DEFF Research Database (Denmark)
2011-01-01
The speech-based envelope power spectrum model (sEPSM) [Jørgensen and Dau (2011). J. Acoust. Soc. Am., 130 (3), 1475–1487] estimates the envelope signal-to-noise ratio (SNRenv) of distorted speech and accurately describes the speech recognition thresholds (SRT) for normal-hearing listeners...... conditions by comparing predictions to measured data from [Kjems et al. (2009). J. Acoust. Soc. Am. 126 (3), 1415-1426] where speech is mixed with four different interferers, including speech-shaped noise, bottle noise, car noise, and cafe noise. The model accounts well for the differences in intelligibility...
Contamination of the Epoch of Reionization power spectrum in the presence of foregrounds
Sims, Peter H; Alexander, Paul; Carilli, Chris L
2016-01-01
We construct foreground simulations comprising spatially correlated extragalactic and diffuse Galactic emission components and calculate the `intrinsic' (instrument-free) two-dimensional spatial power spectrum and the cylindrically and spherically averaged three-dimensional k-space power spectra of the Epoch of Reionization (EoR) and our foreground simulations using a Bayesian power spectral estimation framework. This leads us to identify a model dependent region of optimal signal estimation for our foreground and EoR models, within which the spatial power in the EoR signal relative to foregrounds is maximised. We identify a target field dependent region, in k-space, of intrinsic foreground power spectral contamination at low k_perp and k_parallel and a transition to a relatively foreground-free intrinsic EoR window in the complement to this region. The contaminated region of k-space demonstrates that simultaneous estimation of the EoR and foregrounds is important for obtaining statistically robust estimates ...
Developmental trajectories of resting EEG power: an endophenotype of autism spectrum disorder.
Directory of Open Access Journals (Sweden)
Adrienne L Tierney
Full Text Available Current research suggests that autism spectrum disorder (ASD is characterized by asynchronous neural oscillations. However, it is unclear whether changes in neural oscillations represent an index of the disorder or are shared more broadly among both affected and unaffected family members. Additionally, it remains unclear how early these differences emerge in development and whether they remain constant or change over time. In this study we examined developmental trajectories in spectral power in infants at high- or low-risk for ASD. Spectral power was extracted from resting EEG recorded over frontal regions of the scalp when infants were 6, 9, 12, 18 and 24 months of age. We used multilevel modeling to assess change over time between risk groups in the delta, theta, low alpha, high alpha, beta, and gamma frequency bands. The results indicated that across all bands, spectral power was lower in high-risk infants as compared to low-risk infants at 6-months of age. Furthermore high-risk infants showed different trajectories of change in spectral power in the subsequent developmental window indicating that not only are the patterns of change different, but that group differences are dynamic within the first two years of life. These findings remained the same after removing data from a subset of participants who displayed ASD related behaviors at 24 or 36 months. These differences in the nature of the trajectories of EEG power represent important endophenotypes of ASD.
Directory of Open Access Journals (Sweden)
Benjamin eDummer
2014-09-01
Full Text Available A major source of random variability in cortical networks is the quasi-random arrival of presynaptic action potentials from many other cells. In network studies as well as in the study of the response properties of single cells embedded in a network, synaptic background input is often approximated by Poissonian spike trains. However, the output statistics of the cells is in most cases far from being Poisson. This is inconsistent with the assumption of similar spike-train statistics for pre- and postsynaptic cells in a recurrent network. Here we tackle this problem for the popular class of integrate-and-fire neurons and study a self-consistent statistics of input and output spectra of neural spike trains. Instead of actually using a large network, we use an iterative scheme, in which we simulate a single neuron over several generations. In each of these generations, the neuron is stimulated with surrogate stochastic input that has a similar statistics as the output of the previous generation. For the surrogate input, we employ two distinct approximations: (i a superposition of renewal spike trains with the same interspike interval density as observed in the previous generation and (ii a Gaussian current with a power spectrum proportional to that observed in the previous generation. For input parameters that correspond to balanced input in the network, both the renewal and the Gaussian iteration procedure converge quickly and yield comparable results for the self-consistent spike-train power spectrum. We compare our results to large-scale simulations of a random sparsely connected network of leaky integrate-and-fire neurons (Brunel, J. Comp. Neurosci. 2000 and show that in the asynchronous regime close to a state of balanced synaptic input from the network, our iterative schemes provide excellent approximations to the autocorrelation of spike trains in the recurrent network.
Dummer, Benjamin; Wieland, Stefan; Lindner, Benjamin
2014-01-01
A major source of random variability in cortical networks is the quasi-random arrival of presynaptic action potentials from many other cells. In network studies as well as in the study of the response properties of single cells embedded in a network, synaptic background input is often approximated by Poissonian spike trains. However, the output statistics of the cells is in most cases far from being Poisson. This is inconsistent with the assumption of similar spike-train statistics for pre- and postsynaptic cells in a recurrent network. Here we tackle this problem for the popular class of integrate-and-fire neurons and study a self-consistent statistics of input and output spectra of neural spike trains. Instead of actually using a large network, we use an iterative scheme, in which we simulate a single neuron over several generations. In each of these generations, the neuron is stimulated with surrogate stochastic input that has a similar statistics as the output of the previous generation. For the surrogate input, we employ two distinct approximations: (i) a superposition of renewal spike trains with the same interspike interval density as observed in the previous generation and (ii) a Gaussian current with a power spectrum proportional to that observed in the previous generation. For input parameters that correspond to balanced input in the network, both the renewal and the Gaussian iteration procedure converge quickly and yield comparable results for the self-consistent spike-train power spectrum. We compare our results to large-scale simulations of a random sparsely connected network of leaky integrate-and-fire neurons (Brunel, 2000) and show that in the asynchronous regime close to a state of balanced synaptic input from the network, our iterative schemes provide an excellent approximations to the autocorrelation of spike trains in the recurrent network.
Paciga, Gregory; Bandura, Kevin; Chang, Tzu-Ching; Gupta, Yashwant; Hirata, Christopher; Odegova, Julia; Pen, Ue-Li; Peterson, Jeffrey B; Roy, Jayanta; Shaw, Richard; Sigurdson, Kris; Voytek, Tabitha
2013-01-01
The GMRT Epoch of Reionization (EoR) experiment is an ongoing effort to measure the power spectrum from neutral hydrogen at high redshift. We have previously reported an upper limit of (70 mK)^2 at wavenumbers of k=0.65 h/Mpc using a basic piecewise-linear foreground subtraction. In this paper we explore the use of a singular value decomposition to remove foregrounds with fewer assumptions about the foreground structure. Using this method we also quantify, for the first time, the signal loss due to the foreground filter and present new power spectra adjusted for this loss, providing a revised measurement of a 2-sigma upper limit at (248 mK)^2 for k=0.50 h/Mpc. While this revised limit is larger than previously reported, we believe it to be more robust and still represents the best current constraints on reionization at z=8.6.
Prospects for ACT: simulations, power spectrum, and non-Gaussian analysis
Huffenberger, Kevin M; Huffenberger, Kevin M.; Seljak, Uros
2004-01-01
A new generation of instruments will reveal the microwave sky at high resolution. We focus on one of these, the Atacama Cosmology Telescope, which probes scales 1000
van Engelen, A; Sehgal, N; Holder, G P; Zahn, O; Nagai, D
2013-01-01
The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to ACT and SPT. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on sigma_8 and an uncertainty on the total neutrino mass of approximately 50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 15...
Energy Technology Data Exchange (ETDEWEB)
Araujo, D.; Dumoulin, R. N.; Newburgh, L. B.; Zwart, J. T. L. [Department of Physics and Columbia Astrophysics Laboratory, Columbia University, New York, NY 10027 (United States); Bischoff, C.; Brizius, A.; Buder, I.; Kusaka, A. [Kavli Institute for Cosmological Physics, Department of Physics, Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637 (United States); Chinone, Y. [High Energy Accelerator Research Organization (KEK), 1-1 Oho, Tsukuba, Ibaraki 305-0801 (Japan); Cleary, K.; Reeves, R. [Cahill Center for Astronomy and Astrophysics, California Institute of Technology, 1200 E. California Blvd M/C 249-17, Pasadena, CA 91125 (United States); Monsalve, R.; Bustos, R. [Department of Physics, University of Miami, 1320 Campo Sano Drive, Coral Gables, FL 33146 (United States); Naess, S. K.; Eriksen, H. K. [Institute of Theoretical Astrophysics, University of Oslo, P.O. Box 1029 Blindern, NO-0315 Oslo (Norway); Wehus, I. K. [Department of Astrophysics, University of Oxford, Keble Road, Oxford OX1 3RH (United Kingdom); Bronfman, L. [Departamento de Astronomia, Universidad de Chile, Casilla 36-D, Santiago (Chile); Church, S. E. [Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University, Varian Physics Building, 382 Via Pueblo Mall, Stanford, CA 94305 (United States); Dickinson, C. [Jodrell Bank Centre for Astrophysics, Alan Turing Building, School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester M13 9PL (United Kingdom); Gaier, T., E-mail: ibuder@uchicago.edu [Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States); Collaboration: QUIET Collaboration; and others
2012-12-01
The Q/U Imaging ExperimenT (QUIET) has observed the cosmic microwave background (CMB) at 43 and 95 GHz. The 43 GHz results have been published in a previous paper, and here we report the measurement of CMB polarization power spectra using the 95 GHz data. This data set comprises 5337 hr of observations recorded by an array of 84 polarized coherent receivers with a total array sensitivity of 87 {mu}K{radical}s. Four low-foreground fields were observed, covering a total of {approx}1000 deg{sup 2} with an effective angular resolution of 12.'8, allowing for constraints on primordial gravitational waves and high signal-to-noise measurements of the E-modes across three acoustic peaks. The data reduction was performed using two independent analysis pipelines, one based on a pseudo-C {sub l} (PCL) cross-correlation approach, and the other on a maximum-likelihood (ML) approach. All data selection criteria and filters were modified until a predefined set of null tests had been satisfied before inspecting any non-null power spectrum. The results derived by the two pipelines are in good agreement. We characterize the EE, EB, and BB power spectra between l = 25 and 975 and find that the EE spectrum is consistent with {Lambda}CDM, while the BB power spectrum is consistent with zero. Based on these measurements, we constrain the tensor-to-scalar ratio to r = 1.1{sup +0.9} {sub -0.8} (r < 2.8 at 95% C.L.) as derived by the ML pipeline, and r = 1.2{sup +0.9} {sub -0.8} (r < 2.7 at 95% C.L.) as derived by the PCL pipeline. In one of the fields, we find a correlation with the dust component of the Planck Sky Model, though the corresponding excess power is small compared to statistical errors. Finally, we derive limits on all known systematic errors, and demonstrate that these correspond to a tensor-to-scalar ratio smaller than r = 0.01, the lowest level yet reported in the literature.
Power spectrum analysis of polarized emission from the Canadian galactic plane survey
Energy Technology Data Exchange (ETDEWEB)
Stutz, R. A.; Rosolowsky, E. W. [University of British Columbia Okanagan, 3333 University Way, Kelowna BC, V1V 1V7 (Canada); Kothes, R.; Landecker, T. L. [National Research Council Canada, Dominion Radio Astrophysical Observatory, Box 248, Penticton, BC, V2A 6J9 (Canada)
2014-05-20
Angular power spectra are calculated and presented for the entirety of the Canadian Galactic Plane Survey polarization data set at 1.4 GHz covering an area of 1060 deg{sup 2}. The data analyzed are a combination of data from the 100 m Effelsberg Telescope, the 26 m Telescope at the Dominion Radio Astrophysical Observatory, and the Synthesis Telescope at the Dominion Radio Astrophysical Observatory, allowing all scales to be sampled down to arcminute resolution. The resulting power spectra cover multipoles from ℓ ≈ 60 to ℓ ≈ 10{sup 4} and display both a power-law component at low multipoles and a flattening at high multipoles from point sources. We fit the power spectrum with a model that accounts for these components and instrumental effects. The resulting power-law indices are found to have a mode of 2.3, similar to previous results. However, there are significant regional variations in the index, defying attempts to characterize the emission with a single value. The power-law index is found to increase away from the Galactic plane. A transition from small-scale to large-scale structure is evident at b = 9°, associated with the disk-halo transition in a 15° region around l = 108°. Localized variations in the index are found toward H II regions and supernova remnants, but the interpretation of these variations is inconclusive. The power in the polarized emission is anticorrelated with bright thermal emission (traced by Hα emission) indicating that the thermal emission depolarizes background synchrotron emission.
Morris, J. F. (Inventor)
1985-01-01
This invention is directed to transferring heat from an extremely high temperature source to an electrically isolated lower temperature receiver. The invention is particularly concerned with supplying thermal power to a thermionic converter from a nuclear reactor with electric isolation. Heat from a high temperature heat pipe is transferred through a vacuum or a gap filled with electrically nonconducting gas to a cooler heat pipe. If the receiver requires gratr thermal power density, geometries are used with larger heat pipe areas for transmitting and receiving energy than the area for conducting the heat to the thermionic converter. In this way the heat pipe capability for increasing thermal power densities compensates for the comparative low thermal power densities through the electrically nonconducting gap between the two heat pipes.
E→H mode transition density and power in two types of inductively coupled plasma configuration
Energy Technology Data Exchange (ETDEWEB)
Wang, Jian; Du, Yin-chang; Zhang, Xiao; Zheng, Zhe; Liu, Yu; Xu, Liang; Wang, Pi; Cao, Jin-xiang, E-mail: jxcao@ustc.edu.cn [Department of Modern Physics, University of Science and Technology of China, Hefei, Anhui 230026 (China)
2014-07-15
E → H transition power and density were investigated at various argon pressures in inductively coupled plasma (ICP) in a cylindrical interlaid chamber. The transition power versus the pressure shows a minimum transition power at 4 Pa (ν/ω=1) for argon. Then the transition density hardly changes at low pressures (ν/ω≪1), but it increases clearly when argon pressure exceeds an appropriate value. In addition, both the transition power and transition density are lower in the re-entrant configuration of ICP compared with that in the cylindrical configuration of ICP. The result may be caused from the decrease of stochastic heating in the re-entrant configuration of ICP. This work is useful to understand E → H mode transition and control the transition points in real plasma processes.
2010-07-01
... as specified in 40 CFR 1065.610. This is the maximum in-use engine speed used for calculating the NOX... procedures of 40 CFR part 1065, based on the manufacturer's design and production specifications for the..., power density, and maximum in-use engine speed. 1042.140 Section 1042.140 Protection of...
Directory of Open Access Journals (Sweden)
Hongze Li
2014-01-01
Full Text Available Short-term power load forecasting is one of the most important issues in the economic and reliable operation of electricity power system. Taking the characteristics of randomness, tendency, and periodicity of short-term power load into account, a new method (SSA-AR model which combines the univariate singular spectrum analysis and autoregressive model is proposed. Firstly, the singular spectrum analysis (SSA is employed to decompose and reconstruct the original power load series. Secondly, the autoregressive (AR model is used to forecast based on the reconstructed power load series. The employed data is the hourly power load series of the Mid-Atlantic region in PJM electricity market. Empirical analysis result shows that, compared with the single autoregressive model (AR, SSA-based linear recurrent method (SSA-LRF, and BPNN (backpropagation neural network model, the proposed SSA-AR method has a better performance in terms of short-term power load forecasting.
Power spectrum of nuclear spectra with missing levels and mixed symmetries
Energy Technology Data Exchange (ETDEWEB)
Molina, R.A. [Max-Planck-Institut fuer Physik Komplexer Systeme, Noethnitzer Str. 38, D-01187 Dresden (Germany) and Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain)]. E-mail: molina@iem.cfmac.csic.es; Retamosa, J. [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Munoz, L. [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Relano, A. [Departamento de Fisica Atomica, Molecular y Nuclear, Universidad Complutense de Madrid, E-28040 Madrid (Spain); Instituto de Estructura de la Materia, CSIC, Serrano 123, E-28006 Madrid (Spain); Faleiro, E. [Departamento de Fisica Aplicada, Universidad Politecnica de Madrid, E-28012 (Spain)
2007-01-04
Sequences of energy levels in nuclei are often plagued with missing levels whose number and position are unknown. It is also quite usual that all the quantum numbers of certain levels cannot be experimentally determined, and thus levels of different symmetries are mixed in the same sequence. The analysis of these imperfect spectra (from the point of view of spectral statistics) is unavoidable if one wants to extract some statistical information. The power spectrum of the {delta}{sub q} statistic has emerged in recent years as an important tool for the study of quantum chaos and spectral statistics. We derive analytical expressions for the observed power spectrum in terms of the fraction of observed levels and the number of mixed sequences. These expressions are tested with large shell model spectra simulating realistic experimental situations. A good estimation of the number of mixed symmetries and the fraction of missing levels is obtained by means of a least-squares fit in a wide set of different situations.
Galaxy power spectrum in redshift space: combining perturbation theory with the halo model
Okumura, Teppei; Seljak, Uros; Vlah, Zvonimir; Desjacques, Vincent
2015-01-01
Theoretical modeling of the redshift-space power spectrum of galaxies is crucially important to correctly extract cosmological information from redshift surveys. The task is complicated by the nonlinear biasing and redshift space distortion effects, which change with halo mass, and by the wide distribution of halo masses and their occupations by galaxies. One of the main modeling challenges is the existence of satellite galaxies that have both radial distribution and large virial velocities inside halos, a phenomenon known as the Finger-of-God effect. We present a model for the galaxy power spectrum of in which we decompose a given galaxy sample into central and satellite galaxies and relate different contributions to 1- and 2-halo terms in a halo model. Our primary goal is to ensure that any parameters that we introduce have physically meaningful values, and are not just fitting parameters. For the 2-halo terms we use the previously developed RSD modeling of halos in the context of distribution function and ...
The CMBR ISW and HI 21-cm Cross-correlation Angular Power Spectrum
Sarkar, Tapomoy Guha; Bharadwaj, Somnath
2008-01-01
The late-time growth of large scale structures (LSS) is imprinted in the CMBR anisotropy through the Integrated Sachs Wolfe (ISW) effect. This is perceived to be a very important observational probe of dark energy. Future observations of redshifted 21-cm radiation from the cosmological neutral hydrogen (HI) distribution hold the potential of probing the LSS over a large redshift range. We have investigated the possibility of detecting the ISW through cross-correlations between the CMBR anisotropies and redshifted 21-cm observations. Assuming that the HI traces the dark matter, we find that the ISW-HI cross-correlation angular power spectrum at an angular multipole l is proportional to the dark matter power spectrum evaluated at the comoving wave number l/r, where r is the comoving distance to the redshift from which the HI signal originated. The amplitude of the cross-correlation signal depends on parameters related to the HI distribution and the growth of cosmological perturbations. However the cross-correla...
Perturbation theory, effective field theory, and oscillations in the power spectrum
Vlah, Zvonimir; Chu, Man Yat; Feng, Yu
2015-01-01
We explore the relationship between the nonlinear matter power spectrum and the various Lagrangian and Standard Perturbation Theories (LPT and SPT). We first look at it in the context of one dimensional (1-d) dynamics, where 1LPT is exact at the perturbative level and one can exactly resum the SPT series into the 1LPT power spectrum. Shell crossings lead to non-perturbative effects, and the PT ignorance can be quantified in terms of their ratio, which is also the transfer function squared in the absence of stochasticity. At the order of PT we work, this parametrization is equivalent to the results of effective field theory (EFT), and can thus be expanded in terms of the same parameters. We find that its radius of convergence is larger than the SPT loop expansion. The same EFT parametrization applies to all SPT loop terms and, if stochasticity can be ignored, to all N-point correlators. In 3-d, the LPT structure is considerably more complicated, and we find that LPT models with parametrization motivated by the...
The Effect of Fiber Collisions on the Galaxy Power Spectrum Multipole
Hahn, ChangHoon; Blanton, Michael R; Tinker, Jeremy L; Rodriguez-Torres, Sergio
2016-01-01
Fiber-fed multi-object spectroscopic surveys, with their ability to collect an unprecedented number of redshifts, currently dominate large-scale structure studies. However, physical constraints limit these surveys from successfully collecting redshifts from galaxies too close to each other on the focal plane. This ultimately leads to significant systematic effects on galaxy clustering measurements. Using simulated mock catalogs, we demonstrate that fiber collisions have a significant impact on the power spectrum, $P(k)$, monopole and quadrupole that exceeds sample variance at scales smaller than $k\\sim0.1~h/Mpc$. We present two methods to account for fiber collisions in the power spectrum. The first, statistically reconstructs the clustering of fiber collided galaxy pairs by modeling the distribution of the line-of-sight displacements between them. It also properly accounts for fiber collisions in the shot-noise correction term of the $P(k)$ estimator. Using this method, we recover the true $P(k)$ monopole of...
First Season MWA EoR Power spectrum Results at Redshift 7
Beardsley, A. P.; Hazelton, B. J.; Sullivan, I. S.; Carroll, P.; Barry, N.; Rahimi, M.; Pindor, B.; Trott, C. M.; Line, J.; Jacobs, Daniel C.; Morales, M. F.; Pober, J. C.; Bernardi, G.; Bowman, Judd D.; Busch, M. P.; Briggs, F.; Cappallo, R. J.; Corey, B. E.; de Oliveira-Costa, A.; Dillon, Joshua S.; Emrich, D.; Ewall-Wice, A.; Feng, L.; Gaensler, B. M.; Goeke, R.; Greenhill, L. J.; Hewitt, J. N.; Hurley-Walker, N.; Johnston-Hollitt, M.; Kaplan, D. L.; Kasper, J. C.; Kim, H. S.; Kratzenberg, E.; Lenc, E.; Loeb, A.; Lonsdale, C. J.; Lynch, M. J.; McKinley, B.; McWhirter, S. R.; Mitchell, D. A.; Morgan, E.; Neben, A. R.; Thyagarajan, Nithyanandan; Oberoi, D.; Offringa, A. R.; Ord, S. M.; Paul, S.; Prabu, T.; Procopio, P.; Riding, J.; Rogers, A. E. E.; Roshi, A.; Udaya Shankar, N.; Sethi, Shiv K.; Srivani, K. S.; Subrahmanyan, R.; Tegmark, M.; Tingay, S. J.; Waterson, M.; Wayth, R. B.; Webster, R. L.; Whitney, A. R.; Williams, A.; Williams, C. L.; Wu, C.; Wyithe, J. S. B.
2016-12-01
The Murchison Widefield Array (MWA) has collected hundreds of hours of Epoch of Reionization (EoR) data and now faces the challenge of overcoming foreground and systematic contamination to reduce the data to a cosmological measurement. We introduce several novel analysis techniques, such as cable reflection calibration, hyper-resolution gridding kernels, diffuse foreground model subtraction, and quality control methods. Each change to the analysis pipeline is tested against a two-dimensional power spectrum figure of merit to demonstrate improvement. We incorporate the new techniques into a deep integration of 32 hours of MWA data. This data set is used to place a systematic-limited upper limit on the cosmological power spectrum of {{{Δ }}}2≤slant 2.7× {10}4 mK2 at k = 0.27 h Mpc-1 and z = 7.1, consistent with other published limits, and a modest improvement (factor of 1.4) over previous MWA results. From this deep analysis, we have identified a list of improvements to be made to our EoR data analysis strategies. These improvements will be implemented in the future and detailed in upcoming publications.
A Fast Method For Bounding The CMB Power Spectrum Likelihood Function
Borrill, J
1998-01-01
As the Cosmic Microwave Background (CMB) radiation is observed to higher and higher angular resolution the size of the resulting datasets becomes a serious constraint on their analysis. In particular current algorithms to determine the location of, and curvature at, the peak of the power spectrum likelihood function from a general $N_{p}$-pixel CMB sky map scale as $O(N_{p}^{3})$. Moreover the current best algorithm --- the quadratic estimator --- is a Newton-Raphson iterative scheme and so requires a `sufficiently good' starting point to guarantee convergence to the true maximum. Here we present an algorithm to calculate bounds on the likelihood function at any point in parameter space using Gaussian quadrature and show that, judiciously applied, it scales as only $O(N_{p}^{7/3})$. Although it provides no direct curvature information we show how this approach is well-suited both to estimating cosmological parameters directly and to providing a coarse map of the power spectrum likelihood function from which t...
First Season MWA EoR Power Spectrum Results at Redshift 7
Beardsley, A P; Sullivan, I S; Carroll, P; Barry, N; Rahimi, M; Pindor, B; Trott, C M; Line, J; Jacobs, Daniel C; Morales, M F; Pober, J C; Bernardi, G; Bowman, Judd D; Busch, M P; Briggs, F; Cappallo, R J; Corey, B E; de Oliveira-Costa, A; Dillon, Joshua S; Emrich, D; Ewall-Wice, A; Feng, L; Gaensler, B M; Goeke, R; Greenhill, L J; Hewitt, J N; Hurley-Walker, N; Johnston-Hollitt, M; Kaplan, D L; Kasper, J C; Kim, H S; Kratzenberg, E; Lenc, E; Loeb, A; Lonsdale, C J; Lynch, M J; McKinley, B; McWhirter, S R; Mitchell, D A; Morgan, E; Neben, A R; Thyagarajan, Nithyanandan; Oberoi, D; Offringa, A R; Ord, S M; Paul, S; Prabu, T; Procopio, P; Riding, J; Rogers, A E E; Roshi, A; Shankar, N Udaya; Sethi, Shiv K; Srivani, K S; Subrahmanyan, R; Tegmark, M; Tingay, S J; Waterson, M; Wayth, R B; Webster, R L; Whitney, A R; Williams, A; Williams, C L; Wu, C; Wyithe, J S B
2016-01-01
The Murchison Widefield Array (MWA) has collected hundreds of hours of Epoch of Reionization (EoR) data and now faces the challenge of overcoming foreground and systematic contamination to reduce the data to a cosmological measurement. We introduce several novel analysis techniques such as cable reflection calibration, hyper-resolution gridding kernels, diffuse foreground model subtraction, and quality control methods. Each change to the analysis pipeline is tested against a two dimensional power spectrum figure of merit to demonstrate improvement. We incorporate the new techniques into a deep integration of 32 hours of MWA data. This data set is used to place a systematic-limited upper limit on the cosmological power spectrum of $\\Delta^2 \\leq 2.7 \\times 10^4$ mK$^2$ at $k=0.27$ h~Mpc$^{-1}$ and $z=7.1$, consistent with other published limits, and a modest improvement (factor of 1.4) over previous MWA results. From this deep analysis we have identified a list of improvements to be made to our EoR data analys...
A Fast Method for Power Spectrum and Foreground Analysis for 21 cm Cosmology
Dillon, Joshua S; Tegmark, Max
2012-01-01
We develop and demonstrate an acceleration of the Liu & Tegmark quadratic estimator formalism for inverse variance foreground subtraction and power spectrum estimation in 21 cm tomography from O(N^3) to O(N log N), where N is the number of voxels of data. This technique makes feasible the megavoxel scale analysis necessary for current and upcoming radio interferometers by making only moderately restrictive assumptions about foreground models and survey geometry. We exploit iterative and Monte Carlo techniques and the symmetries of the foreground covariance matrices to quickly estimate the 21 cm brightness temperature power spectrum, P(k_parallel, k_perpendicular), the Fisher information matrix, the error bars, the window functions, and the bias. We also extend the Liu & Tegmark foreground model to include bright point sources with known positions in a way that scales as O[(N log N)(N point sources)] < O(N^5/3). As a first application of our method, we forecast error bars and window functions for th...
Elementary Theoretical Forms for the Spatial Power Spectrum of Earth's Crustal Magnetic Field
Voorhies, C.
1998-01-01
The magnetic field produced by magnetization in Earth's crust and lithosphere can be distinguished from the field produced by electric currents in Earth's core because the spatial magnetic power spectrum of the crustal field differs from that of the core field. Theoretical forms for the spectrum of the crustal field are derived by treating each magnetic domain in the crust as the point source of a dipole field. The geologic null-hypothesis that such moments are uncorrelated is used to obtain the magnetic spectrum expected from a randomly magnetized, or unstructured, spherical crust of negligible thickness. This simplest spectral form is modified to allow for uniform crustal thickness, ellipsoidality, and the polarization of domains by an periodically reversing, geocentric axial dipole field from Earth's core. Such spectra are intended to describe the background crustal field. Magnetic anomalies due to correlated magnetization within coherent geologic structures may well be superimposed upon this background; yet representing each such anomaly with a single point dipole may lead to similar spectral forms. Results from attempts to fit these forms to observational spectra, determined via spherical harmonic analysis of MAGSAT data, are summarized in terms of amplitude, source depth, and misfit. Each theoretical spectrum reduces to a source factor multiplied by the usual exponential function of spherical harmonic degree n due to geometric attenuation with attitude above the source layer. The source factors always vary with n and are approximately proportional to n(exp 3) for degrees 12 through 120. The theoretical spectra are therefore not directly proportional to an exponential function of spherical harmonic degree n. There is no radius at which these spectra are flat, level, or otherwise independent of n.
High power density alkaline fuel cell technology for MMW space burst power
Preston, J. Lawrence, Jr.; Trocciola, John C.; Wertheim, Ronald J.
The use of advanced alkaline regenerative fuel cell energy storage systems to provide 10's to 100's of MWe of sprint (burst) power for 100's of seconds per orbit of SDI weapons platform was studied. Recharge power is supplied by a multimegawatt space based nuclear power system. Regenerative fuel cell energy storage systems offer the potential for significant platform mass reduction by reducing the size and mass of the nuclear power source required. This is because the reactor can be sized for the smaller average power level for the energy storage system, rather than the sprint power level. The regenerative fuel cell is a particularly attractive energy storage device because the fuel cell is essentially a static power conversion device, which results in excellent platform stability for weapon pointing and tracking. Based upon the detailed point design and conceptual layout, the alkaline regenerative fuel cell energy storage system is an attractive choice for integration with a nuclear thermionic system for providing multimegawatt burst power and multi orbit capability.
Separating Fractal and Oscillatory Components in the Power Spectrum of Neurophysiological Signal.
Wen, Haiguang; Liu, Zhongming
2016-01-01
Neurophysiological field-potential signals consist of both arrhythmic and rhythmic patterns indicative of the fractal and oscillatory dynamics arising from likely distinct mechanisms. Here, we present a new method, namely the irregular-resampling auto-spectral analysis (IRASA), to separate fractal and oscillatory components in the power spectrum of neurophysiological signal according to their distinct temporal and spectral characteristics. In this method, we irregularly resampled the neural signal by a set of non-integer factors, and statistically summarized the auto-power spectra of the resampled signals to separate the fractal component from the oscillatory component in the frequency domain. We tested this method on simulated data and demonstrated that IRASA could robustly separate the fractal component from the oscillatory component. In addition, applications of IRASA to macaque electrocorticography and human magnetoencephalography data revealed a greater power-law exponent of fractal dynamics during sleep compared to wakefulness. The temporal fluctuation in the broadband power of the fractal component revealed characteristic dynamics within and across the eyes-closed, eyes-open and sleep states. These results demonstrate the efficacy and potential applications of this method in analyzing electrophysiological signatures of large-scale neural circuit activity. We expect that the proposed method or its future variations would potentially allow for more specific characterization of the differential contributions of oscillatory and fractal dynamics to distributed neural processes underlying various brain functions.
Directory of Open Access Journals (Sweden)
A. B. Mukhtubayev
2015-01-01
Full Text Available We have investigated the back reflections influence on the spectrum for optical radiation source of superluminescent diode type and have provided optimal operating conditions of the radiation source. The feature of the research method is the usage of a fiber polarization controller and an optical mirror coated on the end of an optical fiber. The studies were conducted with two sources of optical radiation: ThorLabs superluminescent diode series S5FC1005SXL and LED module ELED-1550-1-E-9-SM1-FA-CW. It was revealed that at the value of back reflections equal to -13 dB relative to the output power source, a negative impact on power and spectral characteristics of the source with an optical power of 2.3 µW is beginning to appear. It was also confirmed that at the increase of the radiation power by increasing the source pumping current, back reflection influence is exhibiting at a lower level of back reflections. The results obtained need to be considered when designing fiber optic sensors in order to eliminate the effect of back reflections on the sources of optical radiation having been studied in this paper.
Evidence for Power Law in the Spectrum of the Coronal Ly-alpha Line
Telloni, Daniele; Antonucci, Ester; Bruno, Roberto; D'Amicis, Raffaella
Long time series of the intensity of the hydrogen Lyα line revealed the existence of f-2 power spectra in the corona at low and mid latitudes and very close to the Sun, at 1.7 solar radii. These observations are performed with the UltraViolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory (SoHO). A preliminary analysis indicates that this scaling extends for more than a decade and terminates at higher frequencies with a flat spectrum indicating the presence of white-noise fluctuations. The frequency corresponding to the knee which separates these two different spectral regimes moves to lower and lower values for observations performed at higher and higher heliographic latitudes. Low-frequency power spectra with a f-2 dependence may be due rapid changes (jumps) in the time series. If these coherent structures are removed from the time series, hydrogen coronal intensity power spectra seem to show a power law following the f-1 scaling which would suggest that 1/f interplanetary noise originates in corona.
Cortical Serotonin Type-2 Receptor Density in Parents of Children with Autism Spectrum Disorders
Goldberg, Jeremy; Anderson, George M.; Zwaigenbaum, Lonnie; Hall, Geoffrey B. C.; Nahmias, Claude; Thompson, Ann; Szatmari, Peter
2009-01-01
Parents (N = 19) of children with autism spectrum disorders (ASD) and adult controls (N = 17) underwent positron emission tomography (PET) using [[superscript 18]F]setoperone to image cortical serotonin type-2 (5-HT2) receptors. The 5-HT2 binding potentials (BPs) were calculated by ratioing [[superscript 18]F]setoperone intensity in regions of…
Campbell, Abbi; Tincani, Matt
2011-01-01
The Power Card strategy is a strength-based intervention to promote social skills of children with autism spectrum disorders (ASD) by capitalizing on their special interests. Although preliminary studies have shown that the Power Card strategy is a promising approach to teach social skills, additional research is needed. The purpose of this study…
THE POWER SPECTRUM OF THE MILKY WAY: VELOCITY FLUCTUATIONS IN THE GALACTIC DISK
Energy Technology Data Exchange (ETDEWEB)
Bovy, Jo [Institute for Advanced Study, Einstein Drive, Princeton, NJ 08540 (United States); Bird, Jonathan C. [Department of Physics and Astronomy, Vanderbilt University, 6301 Stevenson Center, Nashville, TN 37235 (United States); Pérez, Ana E. García; Majewski, Steven R. [Department of Astronomy, University of Virginia, Charlottesville, VA 22904 (United States); Nidever, David L. [Department of Astronomy, University of Michigan, Ann Arbor, MI 48104 (United States); Zasowski, Gail, E-mail: bovy@ias.edu [Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
2015-02-20
We investigate the kinematics of stars in the mid-plane of the Milky Way (MW) on scales between 25 pc and 10 kpc with data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE), the Radial Velocity Experiment (RAVE), and the Geneva-Copenhagen survey (GCS). Using red-clump (RC) stars in APOGEE, we determine the large-scale line-of-sight velocity field out to 5 kpc from the Sun in (0.75 kpc){sup 2} bins. The solar motion V{sub ☉} {sub –} {sub c} with respect to the circular velocity V{sub c} is the largest contribution to the power on large scales after subtracting an axisymmetric rotation field; we determine the solar motion by minimizing the large-scale power to be V{sub ☉} {sub –} {sub c} = 24 ± 1 (ran.) ± 2 (syst. [V{sub c} ]) ± 5 (syst.[large-scale]) km s{sup –1}, where the systematic uncertainty is due to (1) a conservative 20 km s{sup –1} uncertainty in V{sub c} and (2) the estimated power on unobserved larger scales. Combining the APOGEE peculiar-velocity field with RC stars in RAVE out to 2 kpc from the Sun and with local GCS stars, we determine the power spectrum of residual velocity fluctuations in the MW's disk on scales between 0.2 kpc{sup –1} ≤ k ≤ 40 kpc{sup –1}. Most of the power is contained in a broad peak between 0.2 kpc{sup –1} < k < 0.9 kpc{sup –1}. We investigate the expected power spectrum for various non-axisymmetric perturbations and demonstrate that the central bar with commonly used parameters but of relatively high mass can explain the bulk of velocity fluctuations in the plane of the Galactic disk near the Sun. Streaming motions ≈10 km s{sup –1} on ≳ 3 kpc scales in the MW are in good agreement with observations of external galaxies and directly explain why local determinations of the solar motion are inconsistent with global measurements.
Flexible asymmetric supercapacitors with high energy and high power density in aqueous electrolytes.
Cheng, Yingwen; Zhang, Hongbo; Lu, Songtao; Varanasi, Chakrapani V; Liu, Jie
2013-02-07
Supercapacitors with both high energy and high power densities are critical for many practical applications. In this paper, we discuss the design and demonstrate the fabrication of flexible asymmetric supercapacitors based on nanocomposite electrodes of MnO(2), activated carbon, carbon nanotubes and graphene. The combined unique properties of each of these components enable highly flexible and mechanically strong films that can serve as electrodes directly without using any current collectors or binders. Using these flexible electrodes and a roll-up approach, asymmetric supercapacitors with 2 V working voltage were successfully fabricated. The fabricated device showed excellent rate capability, with 78% of the original capacitance retained when the scan rate was increased from 2 mV s(-1) to 500 mV s(-1). Owing to the unique composite structure, these supercapacitors were able to deliver high energy density (24 W h kg(-1)) under high power density (7.8 kW kg(-1)) conditions. These features could enable supercapacitor based energy storage systems to be very attractive for a variety of critical applications, such as the power sources in hybrid electric vehicles and the back-up powers for wind and solar energy, where both high energy density and high power density are required.
Chang, Zhe; Wang, Sai
2013-01-01
The WMAP and Planck observations show that the quadrupole and octopole orientations of the CMB might align with each other. We reveal that the quadrupole--octopole alignment is a natural implication of the primordial power spectrum in an anisotropic spacetime. The primordial power spectrum is presented with a dipolar modulation. We obtain the privileged plane by employing the "power tensor" technique. At this plane, there is the maximum correlation between quadrupole and octopole. The probability for the alignment is much larger than what in the isotropic universe. We find that this model would lead to deviations from the statistical isotropy only for low--\\(\\ell\\) multipoles.
Progress in High Power Density SOFC Material Development for Aerospace Applications
Cable, Thomas L.; Sofie, Stephen W.; Setlock, John A.; Misra, Ajay K.
2004-01-01
Solid oxide fuel cell (SOFC) systems for aircraft applications require order of magnitude increase in specific power density and long life under aircraft operating conditions. Advanced SOFC materials and fabrication processes are being developed at NASA GRC to increase specific power density and durability of SOFC cell and stack. Initial research efforts for increasing specific power density are directed toward increasing the operating temperature for the SOFC system and reducing the weight of the stack. While significant research is underway to develop anode supported SOFC system operating at temperatures in the range of 650 - 850 C for ground power generation applications, such temperatures may not yield the power densities required for aircraft applications. For electrode-supported cells, SOFC stacks with power densities greater than 1.0 W/sq cm are favorable at temperatures in excess of 900 C. The performance of various commercial and developmental anode supported cells is currently being evaluated in the temperature range of 900 to 1000 C to assess the performance gains and materials reliability. The results from these studies will be presented. Since metal interconnects developed for lower temperature operation are not practical at these high temperatures, advanced perovskite based ceramic interconnects with high electronic conductivity and lower sintering temperatures are being developed. Another option for increasing specific power density of SOFC stacks is to decrease the stack weight. Since the interconnect contributes to a significant portion of the stack weight, considerable weight benefits can be derived by decreasing its thickness. Eliminating the gas channels in the interconnect by engineering the pore structure in both anode and cathode can offer significant reduction in thickness of the ceramic interconnect material. New solid oxide fuel cells are being developed with porous engineered electrode supported structures with a 10 - 20 micron thin
Directory of Open Access Journals (Sweden)
Q. Cheng
2010-10-01
Full Text Available This contribution introduces a fractal filtering technique newly developed on the basis of a spectral energy density vs. area power-law model in the context of multifractal theory. It can be used to map anisotropic singularities of geochemical landscapes created from geochemical concentration values in various surface media such as soils, stream sediments, tills and water. A geochemical landscape can be converted into a Fourier domain in which the spectral energy density is plotted against the area (in wave number units, and the relationship between the spectrum energy density (S and the area (A enclosed by the above-threshold spectrum energy density can be fitted by power-law models. Mixed geochemical landscape patterns can be fitted with different S-A power-law models in the frequency domain. Fractal filters can be defined according to these different S-A models and used to decompose the geochemical patterns into components with different self-similarities. The fractal filtering method was applied to a geochemical dataset from 7,349 stream sediment samples collected from Gejiu mineral district, which is famous for its word-class tin and copper production. Anomalies in three different scales were decomposed from total values of the trace elements As, Sn, Cu, Zn, Pb, and Cd. These anomalies generally correspond to various geological features and geological processes such as sedimentary rocks, intrusions, fault intersections and mineralization.
Toward Low-Cost, High-Energy Density, and High-Power Density Lithium-Ion Batteries
Li, Jianlin; Du, Zhijia; Ruther, Rose E.; AN, Seong Jin; David, Lamuel Abraham; Hays, Kevin; Wood, Marissa; Phillip, Nathan D.; Sheng, Yangping; Mao, Chengyu; Kalnaus, Sergiy; Daniel, Claus; Wood, David L.
2017-06-01
Reducing cost and increasing energy density are two barriers for widespread application of lithium-ion batteries in electric vehicles. Although the cost of electric vehicle batteries has been reduced by 70% from 2008 to 2015, the current battery pack cost (268/kWh in 2015) is still >2 times what the USABC targets (125/kWh). Even though many advancements in cell chemistry have been realized since the lithium-ion battery was first commercialized in 1991, few major breakthroughs have occurred in the past decade. Therefore, future cost reduction will rely on cell manufacturing and broader market acceptance. This article discusses three major aspects for cost reduction: (1) quality control to minimize scrap rate in cell manufacturing; (2) novel electrode processing and engineering to reduce processing cost and increase energy density and throughputs; and (3) material development and optimization for lithium-ion batteries with high-energy density. Insights on increasing energy and power densities of lithium-ion batteries are also addressed.
Toward Low-Cost, High-Energy Density, and High-Power Density Lithium-Ion Batteries
Li, Jianlin; Du, Zhijia; Ruther, Rose E.; AN, Seong Jin; David, Lamuel Abraham; Hays, Kevin; Wood, Marissa; Phillip, Nathan D.; Sheng, Yangping; Mao, Chengyu; Kalnaus, Sergiy; Daniel, Claus; Wood, David L.
2017-09-01
Reducing cost and increasing energy density are two barriers for widespread application of lithium-ion batteries in electric vehicles. Although the cost of electric vehicle batteries has been reduced by 70% from 2008 to 2015, the current battery pack cost (268/kWh in 2015) is still >2 times what the USABC targets (125/kWh). Even though many advancements in cell chemistry have been realized since the lithium-ion battery was first commercialized in 1991, few major breakthroughs have occurred in the past decade. Therefore, future cost reduction will rely on cell manufacturing and broader market acceptance. This article discusses three major aspects for cost reduction: (1) quality control to minimize scrap rate in cell manufacturing; (2) novel electrode processing and engineering to reduce processing cost and increase energy density and throughputs; and (3) material development and optimization for lithium-ion batteries with high-energy density. Insights on increasing energy and power densities of lithium-ion batteries are also addressed.
Energy Technology Data Exchange (ETDEWEB)
Lingen Chen; Junlin Zheng; Fengrui Sun [Naval Univ. of Engineering, Faculty 306, Wuhan (China); Chih Wu [US Naval Academy, Mechanical Engineering Dept., Annapolis, MD (United States)
2001-06-07
In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as the objective for performance analysis and optimisation of an irreversible regenerated closed Brayton cycle coupled to variable-temperature heat reservoirs from the viewpoint of finite time thermodynamics (FTT) or entropy generation minimisation (EGM). The analytical formulae about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible compression and expansion losses in the compressor and turbine, the pressure drop losses at the heater, cooler and regenerator as well as in the piping, and the effect of the finite thermal capacity rate of the heat reservoirs. The obtained results are compared with those results obtained by using the maximum power criterion, and the advantages and disadvantages of maximum power density design are analysed. The maximum power density optimisation is performed in two stages. The first is to search the optimum heat conductance distribution corresponding to the optimum power density among the hot- and cold-side heat exchangers and the regenerator for a fixed total heat exchanger inventory. The second is to search the optimum thermal capacitance rate matching corresponding to the inventory. The second is to search the optimum thermal capacitance rate matching corresponding to the optimum power density between the working fluid and the high-temperature heat source for a fixed ratio of the thermal capacitance rates of two heat reservoirs. The influences of some design parameters, including the effectiveness of the regenerator, the inlet temperature ratio of the heat reservoirs, the effectiveness of the heat exchangers between the working fluid and the heat reservoirs, the efficiencies of the compressor and the turbine, and the pressure recovery coefficient, on the optimum heat conductance
Energy Technology Data Exchange (ETDEWEB)
Lingen Chen; Junlin Zheng; Fengrui Sun [Naval University of Engineering, Wuhan (China). Faculty 306; Chih Wu [US Naval Academy, Annapolis, MD (United States). Mechanical Engineering Dept.
2001-06-07
In this paper, the power density, defined as the ratio of power output to the maximum specific volume in the cycle, is taken as the objective for performance analysis and optimization of an irreversible regenerated closed Brayton cycle coupled to variable-temperature heat reservoirs from the viewpoint of finite time thermodynamics (FTT) or entropy generation minimization (EGM). The analytical formulae about the relations between power density and pressure ratio are derived with the heat resistance losses in the hot- and cold-side heat exchangers and the regenerator, the irreversible compression and expansion losses in the compressor and turbine, the pressure drop losses at the heater, cooler and regenerator as well as in the piping, and the effect of the finite thermal capacity rate of the heat reservoirs. The obtained results are compared with those results obtained by using the maximum power criterion, and the advantages and disadvantages of maximum power density design are analysed. The maximum power density optimization is performed in two stages. The first is to search the optimum beat conductance distribution corresponding to the optimum power density among the hot- and cold-side heat exchangers and the regenerator for a fixed total heat exchanger inventory. The second is to search the optimum thermal capacitance rate matching corresponding to the optimum power density between the working fluid and the high-temperature heat source for a fixed ratio of the thermal capacitance rates of two heat reservoirs. The influences of some design parameters, including the effectiveness of the regenerator, the inlet temperature ratio of the heat reservoirs, the effectiveness of the heat exchangers between the working fluid and the heat reservoirs, the efficiencies of the compressor and the turbine, and the pressure recovery coefficient, on the optimum heat conductance distribution, the optimum thermal capacitance rate matching, and the maximum power density are provided by
Linear perturbation theory for tidal streams and the small-scale CDM power spectrum
Bovy, Jo; Sanders, Jason L
2016-01-01
Tidal streams in the Milky Way are sensitive probes of the population of dark-matter subhalos predicted in cold-dark-matter (CDM) simulations. We present a new calculus for computing the effect of subhalo fly-bys on cold tidal streams based on the action-angle representation of streams. The heart of this calculus is a line-of-parallel-angle approach that calculates the perturbed distribution function of a given stream segment by undoing the effect of all impacts. This approach allows one to compute the perturbed stream density and track in any coordinate system in minutes for realizations of the subhalo distribution down to 10^5 Msun, accounting for the stream's internal dispersion and overlapping impacts. We study the properties of density and track fluctuations with suites of simulations. The one-dimensional density and track power spectra along the stream trace the subhalo mass function, with higher-mass subhalos producing power only on large scales, while lower mass subhalos cause structure on smaller sca...
Blot, L.; Corasaniti, P. S.; Alimi, J.-M.; Reverdy, V.; Rasera, Y.
2015-01-01
The upcoming generation of galaxy surveys will probe the distribution of matter in the Universe with unprecedented accuracy. Measurements of the matter power spectrum at different scales and red shifts will provide stringent constraints on the cosmological parameters. However, on non-linear scales this will require an accurate evaluation of the covariance matrix. Here, we compute the covariance matrix of the three-dimensional matter density power spectrum for the concordance ΛCDM cosmology from an ensemble of N-body simulations of the Dark Energy Universe Simulation - Parallel Universe Runs (DEUS-PUR). This consists of 12 288 realizations of a (656 h-1 Mpc)3 simulation box with 2563 particles. We combine this set with an auxiliary sample of 96 simulations of the same volume with 10243 particles. We find the N-body mass resolution effect to be an important source of systematic errors on the covariance at high redshift and small intermediate scales. We correct for this effect by introducing an empirical statistical method which provide an accurate determination of the covariance matrix over a wide range of scales including the baryon oscillations interval. Contrary to previous studies that used smaller N-body ensembles, we find the power spectrum distribution to significantly deviate from expectations of a Gaussian random density field at k ≳ 0.25 h Mpc-1 and z < 0.5. This suggests that for the finite-volume surveys, an unbiased estimate of the ensemble-averaged band power at these scales and red shifts may require a more careful assessment of non-Gaussian errors than previously considered.
Directory of Open Access Journals (Sweden)
Kurt James Werner
2016-10-01
Full Text Available The magnitude of the Discrete Fourier Transform (DFT of a discrete-time signal has a limited frequency definition. Quadratic interpolation over the three DFT samples surrounding magnitude peaks improves the estimation of parameters (frequency and amplitude of resolved sinusoids beyond that limit. Interpolating on a rescaled magnitude spectrum using a logarithmic scale has been shown to improve those estimates. In this article, we show how to heuristically tune a power scaling parameter to outperform linear and logarithmic scaling at an equivalent computational cost. Although this power scaling factor is computed heuristically rather than analytically, it is shown to depend in a structured way on window parameters. Invariance properties of this family of estimators are studied and the existence of a bias due to noise is shown. Comparing to two state-of-the-art estimators, we show that an optimized power scaling has a lower systematic bias and lower mean-squared-error in noisy conditions for ten out of twelve common windowing functions.
Intramuscular and surface EMG power spectrum from dynamic and static contractions.
Christensen, H; Søgaard, K; Jensen, B R; Finsen, L; Sjøgaard, G
1995-03-01
During sustained static contractions an increase in the root mean square (rms) amplitude and a decrease in mean power frequency (MPF), or median power frequency (MF) of the electromyographic (EMG) signal are indicators for the development of muscle fatigue. However, when studying dynamic contractions the interpretation of these variables has been questioned. Therefore, the purpose was to compare the EMG variables recorded from a non-fatigued muscle during a slow low level dynamic contraction to those during a static contraction of similar force level. Surface and intramuscular EMG registrations were obtained from the brachial biceps muscle during: (a) a static isotonic contraction, (b) a dynamic contraction and (c) a static anisotonic contraction. During contractions (a) and (b) the recruitment pattern was analysed using the precision decomposition method. No differences in rms, MPF or MF between the dynamic and static contractions or between the concentric and eccentric phase of the dynamic contraction were found. Furthermore 60% of the identified motor units were active both in the concentric and the eccentric phase. This indicates that motor control during a slow dynamic contraction at low force level does not influence the power spectrum. We suggest that in occupational studies a possible muscle fatigue development with time can be estimated using EMG recordings from the work tasks.
Delay analysis of a point-to-multipoint spectrum sharing network with CSI based power allocation
Khan, Fahd Ahmed
2012-10-01
In this paper, we analyse the delay performance of a point-to-multipoint cognitive radio network which is sharing the spectrum with a point-to-multipoint primary network. The channel is assumed to be independent but not identically distributed and has Nakagami-m fading. A constraint on the peak transmit power of the secondary user transmitter (SU-Tx) is also considered in addition to the peak interference power constraint. Based on the constraints, a power allocation scheme which requires knowledge of the instantaneous channel state information (CSI) of the interference links is derived. The SU-Tx is assumed to be equipped with a buffer and is modelled using the M/G/1 queueing model. Closed form expressions for the probability distribution function (PDF) and cumulative distribution function (CDF) of the packet transmission time is derived. Using the PDF, the expressions for the moments of transmission time are obtained. In addition, using the moments, the expressions for the performance measures such as the total average waiting time of packets and the average number of packets waiting in the buffer of the SU-Tx are also obtained. Numerical simulations corroborate the theoretical results. © 2012 IEEE.
Effects of horseback riding exercise on the relative alpha power spectrum in the elderly.
Cho, Sung-Hyoun
The present study aimed to identify the effects of horseback riding and mechanical horseback riding exercise on the relative α-power spectrum in the elderly. A total of 31 healthy elderly were randomly divided into horseback riding (n=15) and mechanical horseback riding exercise groups (n=16). The horseback riding exercise program was conducted for 25min twice a week for 12 weeks. Two-way repeated analysis of variance was used to identify the changes in measured variables before the exercise program, and after 6 and 12 weeks of the program. The horseback riding exercise group showed an increase in relative fast alpha power in the background electroencephalogram, and the mechanical horseback riding exercise group showed an increase in relative slow alpha power. Both horseback riding and mechanical horseback riding exercises activated the EEG in all domains, thus increasing concentration and restfulness. The results suggested that horseback riding and mechanical horseback riding exercise may have a positive effect on psychological stability in the elderly. Copyright © 2017 Elsevier B.V. All rights reserved.
The Lyman-alpha Forest Power Spectrum from the Sloan Digital Sky Survey
McDonald, P; Burles, S; Schlegel, D J; Weinberg, D H; Shih, D; Schaye, J; Schneider, D P; Brinkmann, J; Brunner, R J; Fukugita, M; Donald, Patrick Mc; Seljak, Uros; Burles, Scott; Schlegel, David J.; Weinberg, David H.; Shih, David; Schaye, Joop; Schneider, Donald P.; Brunner, Robert J.; Fukugita, Masataka
2004-01-01
We measure the power spectrum, P_F(k,z), of the transmitted flux in the Ly-alpha forest using 3035 high redshift quasar spectra from the Sloan Digital Sky Survey. This sample is almost two orders of magnitude larger than any previously available data set, yielding statistical errors of ~0.6% and ~0.005 on, respectively, the overall amplitude and logarithmic slope of P_F(k,z). This unprecedented statistical power requires a correspondingly careful analysis of the data and of possible systematic contaminations in it. For this purpose we reanalyze the raw spectra to make use of information not preserved by the standard pipeline. We investigate the details of the noise in the data, resolution of the spectrograph, sky subtraction, quasar continuum, and metal absorption. We find that background sources such as metals contribute significantly to the total power and have to be subtracted properly. We also find clear evidence for SiIII correlations with the Ly-alpha forest and suggest a simple model to account for thi...
Szabo, Adam; Koval, A.
2011-01-01
The newly reprocessed high time resolution (11/22 vectors/sec) Wind mission interplanetary magnetic field data and the similar observations made by the MESSENGER spacecraft in the inner heliosphere affords an opportunity to compare magnetic field power spectral density variations as a function of radial distance from the Sun under different solar wind conditions. In the reprocessed Wind Magnetic Field Investigation (MFI) data, the spin tone and its harmonics are greatly reduced that allows the meaningful fitting of power spectra to the approx.2 Hz limit above which digitization noise becomes apparent. The powe'r spectral density is computed and the spectral index is fitted for the MHD and ion inertial regime separately along with the break point between the two for various solar wind conditions. Wind and MESSENGER magnetic fluctuations are compared for times when the two spacecraft are close to radial and Parker field alignment. The functional dependence of the ion inertial spectral index and break point on solar wind plasma and magnetic field conditions will be discussed.
Fang, L Z; Fang, Li-Zhi; Feng, Long-Long
2000-01-01
We present a method of measuring galaxy power spectrum based on the multiresolution analysis of the discrete wavelet transformation (DWT). Since the DWT representation has strong capability of suppressing the off-diagonal components of the covariance for selfsimilar clustering, the DWT covariance for popular models of the cold dark matter cosmogony generally is diagonal, or $j$(scale)-diagonal in the scale range, in which the second scale-scale correlations are weak. In this range, the DWT covariance gives a lossless estimation of the power spectrum, which is equal to the corresponding Fourier power spectrum banded with a logarithmical scaling. In the scale range, in which the scale-scale correlation is significant, the accuracy of a power spectrum detection depends on the scale-scale or band-band correlations. This is, for a precision measurements of the power spectrum, a measurement of the scale-scale or band-band correlations is needed. We show that the DWT covariance can be employed to measuring both the ...
Patients with Rheumatoid Arthritis and Chronic Pain Display Enhanced Alpha Power Density at Rest.
Meneses, Francisco M; Queirós, Fernanda C; Montoya, Pedro; Miranda, José G V; Dubois-Mendes, Selena M; Sá, Katia N; Luz-Santos, Cleber; Baptista, Abrahão F
2016-01-01
Patients with chronic pain due to neuropathy or musculoskeletal injury frequently exhibit reduced alpha and increased theta power densities. However, little is known about electrical brain activity and chronic pain in patients with rheumatoid arthritis (RA). For this purpose, we evaluated power densities of spontaneous electroencephalogram (EEG) band frequencies (delta, theta, alpha, and beta) in females with persistent pain due to RA. This was a cross-sectional study of 21 participants with RA and 21 healthy controls (mean age = 47.20; SD = 10.40). EEG was recorded at rest over 5 min with participant's eyes closed. Twenty electrodes were placed over five brain regions (frontal, central, parietal, temporal, and occipital). Significant differences were observed in depression and anxiety with higher scores in RA participants than healthy controls (p = 0.002). Participants with RA exhibited increased average absolute alpha power density in all brain regions when compared to controls [F (1.39) = 6.39, p = 0.016], as well as increased average relative alpha power density [F (1.39) = 5.82, p = 0.021] in all regions, except the frontal region, controlling for depression/anxiety. Absolute theta power density also increased in the frontal, central, and parietal regions for participants with RA when compared to controls [F (1, 39) = 4.51, p = 0.040], controlling for depression/anxiety. Differences were not exhibited on beta and delta absolute and relative power densities. The diffuse increased alpha may suggest a possible neurogenic mechanism for chronic pain in individuals with RA.
Patients with Rheumatoid Arthritis and Chronic Pain Display Enhanced Alpha Power Density at Rest
Meneses, Francisco M.; Queirós, Fernanda C.; Montoya, Pedro; Miranda, José G. V.; Dubois-Mendes, Selena M.; Sá, Katia N.; Luz-Santos, Cleber; Baptista, Abrahão F.
2016-01-01
Patients with chronic pain due to neuropathy or musculoskeletal injury frequently exhibit reduced alpha and increased theta power densities. However, little is known about electrical brain activity and chronic pain in patients with rheumatoid arthritis (RA). For this purpose, we evaluated power densities of spontaneous electroencephalogram (EEG) band frequencies (delta, theta, alpha, and beta) in females with persistent pain due to RA. This was a cross-sectional study of 21 participants with RA and 21 healthy controls (mean age = 47.20; SD = 10.40). EEG was recorded at rest over 5 min with participant's eyes closed. Twenty electrodes were placed over five brain regions (frontal, central, parietal, temporal, and occipital). Significant differences were observed in depression and anxiety with higher scores in RA participants than healthy controls (p = 0.002). Participants with RA exhibited increased average absolute alpha power density in all brain regions when compared to controls [F(1.39) = 6.39, p = 0.016], as well as increased average relative alpha power density [F(1.39) = 5.82, p = 0.021] in all regions, except the frontal region, controlling for depression/anxiety. Absolute theta power density also increased in the frontal, central, and parietal regions for participants with RA when compared to controls [F(1, 39) = 4.51, p = 0.040], controlling for depression/anxiety. Differences were not exhibited on beta and delta absolute and relative power densities. The diffuse increased alpha may suggest a possible neurogenic mechanism for chronic pain in individuals with RA. PMID:27540360
Heya, Manabu; Awazu, Kunio
2002-04-01
Recrystallization of tooth dentin by the application of mid- infrared (MIR) pulsed-laser irradiation is one candidate for a novel, non-invasive treatment for the prevention of tooth decay. Recrystallized dentin functions in a similar way to dental enamel. To recrystallize the dentin effectively and non-invasively it is essential to estimate quantitatively and qualitatively the laser parameters, such as the wavelength and the average power density, required for recrystallization. The laser-tissue interaction is initiated effectively by selective excitation of phosphate acid ions (PO4) in the dentin. Using a tunable, MIR Free Electron Laser (FEL) in the wavelength region of 8.8- 10.6micrometers , corresponding to intense absorption bands due to PO4 vibration modes, we have investigated macroscopically extent of surface modification of dentin, and we have obtained experimental results related to the ablation depth, the MIR absorption spectrum, and the elemental chemical composition. From these results, it was found that (1) the laser parameters at which efficient surface modification, without enhanced ablation effects, occurred were estimated to be approximately in the wavelength and average power density regions of ~9.4- 10.3micrometers and ~10-20 W/cm2, and that (2) in this region PO4 vibration modes with lower binding energy were preferentially excluded from the dentin.
Low density, microcellular, dopable, agar/gelatin foams for pulsed power experiments
Energy Technology Data Exchange (ETDEWEB)
McNamara, W.F. [Orion International Technologies, Inc., Albuquerque, NM (United States); Aubert, J.H. [Sandia National Lab., Albuquerque, NM (United States)
1997-04-01
Low-density, microcellular foams prepared from the natural polymers agar and gelatin have been developed for pulsed-power physics experiments. Numerous experiments were supported with foams having densities at or below 10 mg/cm{sup 3}. For some of the experiments, the agar/gelatin foam was uniformly doped with metallic elements using soluble salts. Depending on the method of preparation, cell sizes were typically below 10 microns and for one process were below 1.0 micron.
The power spectra of CMB and density fluctuations seeded by local cosmic strings
Contaldi, C; Magueijo, J; Contaldi, Carlo; Hindmarsh, Mark; Magueijo, Joao
1999-01-01
We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far to evaluate the two-point functions of their stress energy tensor. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor dominate over vector and tensor components. This result has far reaching consequences. We find that cosmic strings exhibit a single Doppler peak of acceptable height at high although the CDM power spectrum in the ``standard'' cosmology (flat geometry, zero cosmological constant, 5% baryonic component) is the wrong shape to fit large scale structure data.
NASA Glenn Research Center Program in High Power Density Motors for Aeropropulsion
Brown, Gerald V.; Kascak, Albert F.; Ebihara, Ben; Johnson, Dexter; Choi, Benjamin; Siebert, Mark; Buccieri, Carl
2005-01-01
Electric drive of transport-sized aircraft propulsors, with electric power generated by fuel cells or turbo-generators, will require electric motors with much higher power density than conventional room-temperature machines. Cryogenic cooling of the motor windings by the liquid hydrogen fuel offers a possible solution, enabling motors with higher power density than turbine engines. Some context on weights of various systems, which is required to assess the problem, is presented. This context includes a survey of turbine engine weights over a considerable size range, a correlation of gear box weights and some examples of conventional and advanced electric motor weights. The NASA Glenn Research Center program for high power density motors is outlined and some technical results to date are presented. These results include current densities of 5,000 A per square centimeter current density achieved in cryogenic coils, finite element predictions compared to measurements of torque production in a switched reluctance motor, and initial tests of a cryogenic switched reluctance motor.
Zheng, Jianyu; Wang, Hui; Fu, Jianbin; Wei, Li; Pan, Shilong; Wang, Lixian; Liu, Jianguo; Zhu, Ninghua
2014-03-10
A fiber-distributed Ultra-wideband (UWB) noise radar was achieved, which consists of a chaotic UWB noise source based on optoelectronic oscillator (OEO), a fiber-distributed transmission link, a colorless base station (BS), and a cross-correlation processing module. Due to a polarization modulation based microwave photonic filter and an electrical UWB pass-band filter embedded in the feedback loop of the OEO, the power spectrum of chaotic UWB signal could be shaped and notch-filtered to avoid the spectrum-overlay-induced interference to the narrow band signals. Meanwhile, the wavelength-reusing could be implemented in the BS by means of the distributed polarization modulation-to-intensity modulation conversion. The experimental comparison for range finding was carried out as the chaotic UWB signal was notch-filtered at 5.2 GHz and 7.8 GHz or not. Measured results indicate that space resolution with cm-level could be realized after 3-km fiber transmission thanks to the excellent self-correlation property of the UWB noise signal provided by the OEO. The performance deterioration of the radar raised by the energy loss of the notch-filtered noise signal was negligible.
First X-ray observations of Low-Power Compact Steep Spectrum Sources
Kunert-Bajraszewska, M; Siemiginowska, A; Guainazzi, M
2013-01-01
We report first X-ray Chandra observations of a sample of seven low luminosity compact (LLC) sources. They belong to a class of young compact steep spectrum (CSS) radio sources. Four of them have been detected, the other three have upper limit estimations for X-ray flux, one CSS galaxy is associated with an X-ray cluster. We have used the new observations together with the observational data for known strong CSS and gigahertz-peaked spectrum (GPS) objects and large scale FRIs and FRIIs to study the relation between morphology, X-ray properties and excitation modes in radio-loud AGNs. We found that: (1) The low power objects fit well to the already established X-ray - radio luminosity correlation for AGNs and occupy the space among, weaker in the X-rays, FRI objects. (2) The high excitation galaxies (HEG) and low excitation galaxies (LEG) occupy distinct locus in the radio/X-ray luminosity plane, notwithstanding their evolutionary stage. This is in agreement with the postulated different origin of the X-ray em...
Intercomparison of methods for image quality characterization. II. Noise power spectrum.
Dobbins, James T; Samei, Ehsan; Ranger, Nicole T; Chen, Ying
2006-05-01
Second in a two-part series comparing measurement techniques for the assessment of basic image quality metrics in digital radiography, in this paper we focus on the measurement of the image noise power spectrum (NPS). Three methods were considered: (1) a method published by Dobbins et al. [Med. Phys. 22, 1581-1593 (1995)], (2) a method published by Samei et al. [Med. Phys. 30, 608-622 (2003)], and (3) a new method sanctioned by the International Electrotechnical Commission (IEC 62220-1, 2003), developed as part of an international standard for the measurement of detective quantum efficiency. In addition to an overall comparison of the estimated NPS between the three techniques, the following factors were also evaluated for their effect on the measured NPS: horizontal versus vertical directional dependence, the use of beam-limiting apertures, beam spectrum, and computational methods of NPS analysis, including the region-of-interest (ROI) size and the method of ROI normalization. Of these factors, none was found to demonstrate a substantial impact on the amplitude of the NPS estimates ( 0.15 mm(-1).
Reconstruction of the primordial power spectrum of curvature perturbations using multiple data sets
Hunt, Paul
2014-01-01
Detailed knowledge of the primordial power spectrum (PPS) of curvature perturbations is essential both in order to elucidate the physical mechanism (`inflation') which generated it, and for estimating the parameters of the assumed cosmological model from CMB and LSS data. Hence it ought to be extracted from such data in a model-independent manner, however this is difficult because relevant cosmological observables are given in general by a convolution of the PPS with some smoothing kernel. The deconvolution problem is ill-conditioned so a regularisation scheme must be employed to control error propagation. We demonstrate that `Tikhonov regularisation' can robustly reconstruct the PPS from multiple cosmological data sets, a significant advantage being that both its uncertainty and resolution are precisely quantified. Using Monte Carlo simulations we investigate the performance of several regularisation parameter selection methods and find that generalised cross-validation and Mallow's C_p method give optimal r...
Frequency Spectrum Based Low-Area Low-Power Parallel FIR Filter Design
Directory of Open Access Journals (Sweden)
Jin-Gyun Chung
2002-09-01
Full Text Available Parallel (or block FIR digital filters can be used either for high-speed or low-power (with reduced supply voltage applications. Traditional parallel filter implementations cause linear increase in the hardware cost with respect to the block size. Recently, an efficient parallel FIR filter implementation technique requiring a less-than linear increase in the hardware cost was proposed. This paper makes two contributions. First, the filter spectrum characteristics are exploited to select the best fast filter structures. Second, a novel block filter quantization algorithm is introduced. Using filter benchmarks, it is shown that the use of the appropriate fast FIR filter structures and the proposed quantization scheme can result in reduction in the number of binary adders up to 20%.
Power spectrum oscillations from Planck-suppressed operators in monodromy inflation
Price, Layne C
2015-01-01
We consider a phenomenological model of monodromy inflation where the inflaton is the phase of a complex scalar field $\\Phi$. Planck-suppressed operators of $\\mathcal O(f^5/M_\\mathrm{pl})$ modify the geometry of the vev $\\left \\langle \\Phi \\right \\rangle$ at first order in the decay constant $f$, which adds a first-order periodic term to the definition of the canonically normalized inflaton $\\phi$. This correction to the inflaton induces a fixed number of extra oscillatory terms in the monodromy potential $V \\sim \\theta^p$. We derive the same result in a toy scenario where the vacuum $\\left \\langle \\Phi \\right \\rangle$ is an ellipse with an arbitrarily large eccentricity. These extra oscillations change the form of the power spectrum as a function of scale $k$ and provide a possible mechanism for differentiating EFT-motivated monodromy inflation from models where the angular shift symmetry is a gauge symmetry.
Rolling Element Bearing Fault Diagnosis Using Laplace-Wavelet Envelope Power Spectrum
Directory of Open Access Journals (Sweden)
D. K. Harrison
2007-01-01
Full Text Available The bearing characteristic frequencies (BCF contain very little energy, and are usually overwhelmed by noise and higher levels of macro-structural vibrations. They are difficult to find in their frequency spectra when using the common technique of fast fourier transforms (FFT. Therefore, Envelope Detection (ED has always been used with FFT to identify faults occurring at the BCF. However, the computation of the ED is suffering to strictly define the resonance frequency band. In this paper, an alternative approach based on the Laplace-wavelet enveloped power spectrum is proposed. The Laplace-Wavelet shape parameters are optimized based on Kurtosis maximization criteria. The results for simulated as well as real bearing vibration signal show the effectiveness of the proposed method to extract the bearing fault characteristic frequencies from the resonant frequency band.
Power Allocation and Spectrum Sharing in Multi-User, Multi-Channel Systems with Strategic Users
Kakhbod, Ali
2010-01-01
We consider the decentralized power allocation and spectrum sharing problem in multi-user, multi-channel systems with strategic users. We present a mechanism/game form that has the following desirable features. (1) It is individually rational. (2) It is budget balanced at every Nash equilibrium of the game induced by the game form as well as off equilibrium. (3) The allocation corresponding to every Nash equilibrium (NE) of the game induced by the mechanism is a Lindahl allocation, that is a weakly Pareto optimal allocation. Our proposed game form/mechanism achieves all the above desirable properties without any assumption about, concavity, differentiability, monotonicity, or quasi-linearity of the users' utility functions.
Fourier Power Spectrum Analysis of Exons for the Period-3 Behavior
Institute of Scientific and Technical Information of China (English)
Yuan Xin TIAN; Chao CHEN; Xiao Yong ZOU; Jian Ding QIU; Pei Xiang CAI; Jin Yuan MO
2005-01-01
The period-3 behaviors of 105 exons from 20 genes in human were studied by Fourier power spectrum. The results indicated that not all exons show the period-3 behavior. The exons were adjusted in order to make them accord with the order of the protein translated, and we found that the period-3 character is relation to the length of exons and the bases distribution in the three codon position. Furthermore, as long as the exons with period-3 behavior accord with the order of protein translated, they would exhibit the synonymous codons usage preference, and the codons with g/c at the third position are used in higher frequency. The results are significant to the gene prediction and the research on the introns.
Liu, Adrian
2015-01-01
Improvements in current instruments and the advent of next-generation instruments will soon push observational 21 cm cosmology into a new era, with high significance measurements of both the power spectrum and the mean ("global") signal of the 21 cm brightness temperature. In this paper we use the recently commenced Hydrogen Epoch of Reionization Array as a worked example to provide forecasts on astrophysical and cosmological parameter constraints. In doing so we improve upon previous forecasts in a number of ways. First, we provide updated forecasts using the latest best-fit cosmological parameters from the Planck satellite, exploring the impact of different Planck datasets on 21 cm experiments. We also show that despite the exquisite constraints that other probes have placed on cosmological parameters, the remaining uncertainties are still large enough to have a non-negligible impact on upcoming 21 cm data analyses. While this complicates high-precision constraints on reionization models, it provides an ave...
Chang, Zhe
2014-01-01
We propose the gravity's rainbow scenario as a possible alternative of the inflation paradigm to account for the flatness and horizon problems. We focus on studying the cosmological scalar perturbations which are seeded by the quantum fluctuations in the very early universe. The scalar power spectrum is expected to be nearly scale-invariant. We estimate the rainbow index $\\lambda$ and energy scale $M$ in the gravity's rainbow scenario by analyzing the Planck temperature and WMAP polarization datasets. The constraints on them are given by $\\lambda=2.933\\pm0.012$ and $\\ln (10^5M/M_p)= -0.401^{+0.457}_{-0.451}$ at the $68\\%$ confidence level.
Choudhuri, Samir; Ghosh, Abhik; Ali, SK Saiyad
2014-01-01
We present two estimators to quantify the angular power spectrum of the sky signal directly from the visibilities measured in radio interferometric observations. This is relevant for both the foregrounds and the cosmological 21-cm signal buried therein. The discussion here is restricted to the Galactic synchrotron radiation, the most dominant foreground component after point source removal. Our theoretical analysis is validated using simulations at 150 MHz, mainly for GMRT and also briefly for LOFAR. The Bare Estimator uses pairwise correlations of the measured visibilities, while the Tapered Gridded Estimator uses the visibilities after gridding in the uv plane. The former is very precise, but computationally expensive for large data. The latter has a lower precision, but takes less computation time which is proportional to the data volume. The latter also allows tapering of the sky response leading to sidelobe suppression, an useful ingredient for foreground removal. Both estimators avoid the positive bias ...
Super-Survey Tidal Effect on Redshift-space Power Spectrum
Akitsu, Kazuyuki; Li, Yin
2016-01-01
Long-wavelength matter inhomogeneities contain cleaner information on the nature of primordial perturbations as well as the physics of the early universe. The large-scale coherent overdensity and tidal force, not directly observable for a finite-volume galaxy survey, are both related to the Hessian matrix of large-scale gravitational potential and therefore of equal importance. We show that the coherent tidal force causes a homogeneous anisotropic distortion of the observed distribution of galaxies in all three directions, perpendicular and parallel to the line-of-sight direction. This effect mimics the redshift-space distortion signal of galaxy peculiar velocities, as well as a distortion by the Alcock-Paczynski effect. We quantify its impact on the redshift-space power spectrum to the leading order, and discuss its importance for the ongoing and upcoming galaxy surveys.
Linear perturbation theory for tidal streams and the small-scale CDM power spectrum
Bovy, Jo; Erkal, Denis; Sanders, Jason L.
2017-04-01
Tidal streams in the Milky Way are sensitive probes of the population of low-mass dark matter subhaloes predicted in cold dark matter (CDM) simulations. We present a new calculus for computing the effect of subhalo fly-bys on cold streams based on the action-angle representation of streams. The heart of this calculus is a line-of-parallel-angle approach that calculates the perturbed distribution function of a stream segment by undoing the effect of all relevant impacts. This approach allows one to compute the perturbed stream density and track in any coordinate system in minutes for realizations of the subhalo distribution down to 105 M⊙, accounting for the stream's internal dispersion and overlapping impacts. We study the statistical properties of density and track fluctuations with large suites of simulations of the effect of subhalo fly-bys. The one-dimensional density and track power spectra along the stream trace the subhalo mass function, with higher mass subhaloes producing power only on large scales, while lower mass subhaloes cause structure on smaller scales. We also find significant density and track bispectra that are observationally accessible. We further demonstrate that different projections of the track all reflect the same pattern of perturbations, facilitating their observational measurement. We apply this formalism to data for the Pal 5 stream and make a first rigorous determination of 10^{+11}_{-6} dark matter subhaloes with masses between 106.5 and 109 M⊙ within 20 kpc from the Galactic centre [corresponding to 1.4^{+1.6}_{-0.9} times the number predicted by CDM-only simulations or to fsub(r measurements of the subhalo mass function down to 105 M⊙, thus definitively testing whether dark matter is clumpy on the smallest scales relevant for galaxy formation.
A High Power Density Integrated Charger for Electric Vehicles with Active Ripple Compensation
Directory of Open Access Journals (Sweden)
Liwen Pan
2015-01-01
Full Text Available This paper suggests a high power density on-board integrated charger with active ripple compensation circuit for electric vehicles. To obtain a high power density and high efficiency, silicon carbide devices are reported to meet the requirement of high-switching-frequency operation. An integrated bidirectional converter is proposed to function as AC/DC battery charger and to transfer energy between battery pack and motor drive of the traction system. In addition, the conventional H-bridge circuit suffers from ripple power pulsating at second-order line frequency, and a scheme of active ripple compensation circuit has been explored to solve this second-order ripple problem, in which a pair of power switches shared traction mode, a ripple energy storage capacitor, and an energy transfer inductor. Simulation results in MATLAB/Simulink validated the eligibility of the proposed topology. The integrated charger can work as a 70 kW motor drive circuit or a converter with an active ripple compensation circuit for 3 kW charging the battery. The impact of the proposed topology and control strategy on the integrated charger power losses, efficiency, power density, and thermal performance has also been analysed and simulated.
Bouleux, Guillaume
2013-12-01
Diagnosing defects on rotating machines can be reached by several angles. When dealing with asynchronous motor drive, such physical elements rotate that a natural angle for treating the healthiness of the motor can be obtained by the use of spectral analysis tools. It is now stated that electrical or mechanical defects, which appear periodically as well, can be retrieved by analyzing the amplitude of particular frequencies inside an estimated power spectrum. When dealing with broken rotor bars detection it is essential to accurately localize the frequencies related to the slip inside the power spectrum. The diagnosis is thereafter made by indicators given with respect to their power. For actual low level of load operations, the supply frequency generally masks the frequencies which could be exploited for indicators. Therefore, we propose to cancel, as well as possible, the contribution of this supply frequency to develop the useful and closely components. The resolution should be very thin for the components to be estimated. In consequence, we use a prior-knowledge subspace-based frequency estimator, already developed in the literature, we complete with an Oblique Projection coupled with a Total Least Squares solution for estimating the power of the resulting estimated frequencies. Finally, we show by means of a real application how it contributes to improve the power spectrum estimation when compared to the FFT or periodogram-based analysis and how the aforementioned power spectrum makes the diagnosis indicator of rotor bars efficient.
Warm dark matter signatures on the 21cm power spectrum: Intensity mapping forecasts for SKA
Carucci, Isabella P; Viel, Matteo; Lapi, Andrea
2015-01-01
We investigate the impact that warm dark matter (WDM) has in terms of 21cm intensity mapping in the post-reionization Universe at z = 3 - 5. We perform hydrodynamic simulations for 5 different models: cold dark matter and WDM with 1,2,3,4 keV (thermal relic) mass and assign the neutral hydrogen a-posteriori using two different methods that both reproduce observations in terms of column density distribution function of neutral hydrogen systems. Contrary to naive expectations, the suppression of power present in the linear and non-linear matter power spectra, results in an increase of power in terms of neutral hydrogen and 21cm power spectra. This is due to the fact that there is a lack of small mass halos in WDM models with respect to cold dark matter: in order to distribute a total amount of neutral hydrogen within the two cosmological models, a larger quantity has to be placed in the most massive halos, that are more biased compared to the cold dark matter cosmology. We quantify this effect and address signi...
Gaspari, M; Nagai, D; Lau, E T; Zhuravleva, I
2014-01-01
Exploring the ICM power spectrum can help us to probe the physics of galaxy clusters. Using high-resolution 3D plasma simulations, we study the statistics of the velocity field and its relation with the thermodynamic perturbations. The normalization of the ICM spectrum (density, entropy, or pressure) is linearly tied to the level of large-scale motions, which excite both gravity and sound waves due to stratification. For low 3D Mach number M~0.25, gravity waves mainly drive entropy perturbations, traced by preferentially tangential turbulence. For M>0.5, sound waves start to significantly contribute, passing the leading role to compressive pressure fluctuations, associated with isotropic turbulence (or a slight radial bias). Density and temperature fluctuations are then characterized by the dominant process: isobaric (low M), adiabatic (high M), or isothermal (strong conduction). Most clusters reside in the intermediate regime, showing a mixture of gravity and sound waves, hence drifting towards isotropic vel...
Interpreting the power spectrum of Dansgaard-Oeschger events via stochastic dynamical systems
Mitsui, Takahito; Lenoir, Guillaume; Crucifix, Michel
2017-04-01
Dansgaard-Oeschger (DO) events are abrupt climate shifts, which are particularly pronounced in the North Atlantic region during glacial periods [Dansgaard et al. 1993]. The signals are most clearly found in δ 18O or log [Ca2+] records of Greenland ice cores. The power spectrum S(f) of DO events has attracted attention over two decades with debates on the apparent 1.5-kyr periodicity [Grootes & Stuiver 1997; Schultz et al. 2002; Ditlevsen et al. 2007] and scaling property over several time scales [Schmitt, Lovejoy, & Schertzer 1995; Rypdal & Rypdal 2016]. The scaling property is written most simply as S(f)˜ f-β , β ≈ 1.4. However, physical as well as underlying dynamics of the periodicity and the scaling property are still not clear. Pioneering works for modelling the spectrum of DO events are done by Cessi (1994) and Ditlevsen (1999), but their model-data comparisons of the spectra are rather qualitative. Here, we show that simple stochastic dynamical systems can generate power spectra statistically consistent with the observed spectra over a wide range of frequency from orbital to the Nyquist frequency (=1/40 yr-1). We characterize the scaling property of the spectrum by defining a local scaling exponentβ _loc. For the NGRIP log [Ca2+] record, the local scaling exponent β _loc increases from ˜ 1 to ˜ 2 as the frequency increases from ˜ 1/5000 yr-1 to ˜ 1/500 yr-1, and β _loc decreases toward zero as the frequency increases from ˜ 1/500 yr-1 to the Nyquist frequency. For the δ 18O record, the local scaling exponent β _loc increases from ˜ 1 to ˜ 1.5 as the frequency increases from ˜ 1/5000 yr^{-1 to ˜ 1/1000 yr-1, and β _loc decreases toward zero as the frequency increases from ˜ 1/1000 yr-1 to the Nyquist frequency. This systematic breaking of a single scaling is reproduced by the simple stochastic models. Especially, the models suggest that the flattening of the spectra starting from multi-centennial scale and ending at the Nyquist frequency
Constraints on the High-l Power Spectrum of Millimeter-wave Anisotropies from APEX-SZ
Reichardt, C L; Ade, P A R; Basu, K; Bender, A N; Bertoldi, F; Cho, H -M; Chon, G; Dobbs, M; Ferrusca, D; Halverson, N W; Holzapfel, W L; Horellou, C; Johansson, D; Johnson, B R; Kennedy, J; Kneissl, R; Lanting, T; Lee, A T; Lueker, M; Mehl, J; Menten, K M; Nord, M; Pacaud, F; Richards, P L; Schaaf, R; Schwan, D; Spieler, H; Weiss, A; Westbrook, B
2009-01-01
We present measurements of the angular power spectrum of millimeter wave anisotropies with the APEX-SZ instrument. APEX-SZ has mapped 0.8 square degrees of sky at a frequency of 150 GHz with an angular resolution of 1'. These new measurements significantly improve the power constraints at 150 GHz over the range of angular multipoles 3000 < l < 10,000, limiting the total astronomical anisotropy in a flat band power to be less than 105 microK^2 at 95% CL. We expect both submillimeter-bright, dusty galaxies and secondary CMB anisotropies from the Sunyaev-Zel'dovich effect (SZE) to significantly contribute to the observed power. Subtracting the SZE power spectrum expected for sigma_8=0.8 and masking bright sources, the best fit value for the remaining power is C_l = 1.1^{+0.9}_{-0.8} x 10^{-5} micro K^2 (1.7^{+1.4}_{-1.3} Jy^2 sr^{-1}). This agrees well with model predictions for power due to submillimeter-bright, dusty galaxies. Simultaneously fitting for the amplitude of the SZE power spectrum and a Poiss...
Deng, Y; Tian, X; Chen, B Y; Zhou, N; Xia, M; Bai, W W; Dou, M M; Liu, X Y
2017-04-12
Objective: To investigate the variation of electroencephalograph(EEG) power density during different sleep stages in OSA for understanding of the mechanisms underlying the brain dysfunction in OSA as well as its earlier diagnosis and treatment. Methods: Sixteen-channel EEGs from OSA patients and normal controls in stage wake, sleep stage 1, sleep stage 2, sleep stage 3 and rapid eye movement stage were analyzed by time-frequency analysis method. The EEG power density in different frequency bands (including δ, θ, α, σ, β and γ) was respectively compared between the 2 groups. The correlation between the variation in the EEG power and primary indices of polysomnography was further analyzed. Results: The EEG power density in δ band in stage wake [OSA: (0.82±0.13) μV(2)/Hz, Control: (0.66±0.02) μV(2)/Hz, t=4.309, Pdensity was significantly higher in frontal and central regions in stage wake [frontal: OSA: (0.90±0.02) μV(2)/Hz, Control: (0.66±0.02) μV(2)/Hz, t=8.539, Pdensity in central region in stage 1 and stage 3 was positively correlated with arousal index (r=0.877 in stage 1, 0.656 in stage 3), implying that sleep fragmentation was closely related to the variation of EEG power density during nocturnal sleep in OSA. Conclusions: The feature stages for OSA are stage wake, stage 1 and stage 3. The EEG power density in OSA (δ band) was significantly higher than that in the control. The EEG power density in OSA and the control shows differences in frontal and central regions in stage wake and stage 1, as well as in central region in stage 3. The results indicate that low-frequency EEG power density giving priority to frontal area and central area has improved in severe OSA, which may be related to the neurologic deficits in corresponding brain areas.
Pechacek, Tomas; Karas, Vladimir; Czerny, Bozena; Dovciak, Michal
2013-01-01
We study some general properties of accretion disc variability in the context of stationary random processes. In particular, we are interested in mathematical constraints that can be imposed on the functional form of the Fourier power-spectrum density (PSD) that exhibits a multiply broken shape and several local maxima. We develop a methodology for determining the regions of the model parameter space that can in principle reproduce a PSD shape with a given number and position of local peaks and breaks of the PSD slope. Given the vast space of possible parameters, it is an important requirement that the method is fast in estimating the PSD shape for a given parameter set of the model. We generated and discuss the theoretical PSD profiles of a shot-noise-type random process with exponentially decaying flares. Then we determined conditions under which one, two, or more breaks or local maxima occur in the PSD. We calculated positions of these features and determined the changing slope of the model PSD. Furthermor...
Akselrod, Solange; Gordon, David; Ubel, F. Andrew; Shannon, Daniel C.; Barger, A. Clifford; Cohen, Richard J.
1981-07-01
Power spectrum analysis of heart rate fluctuations provides a quantitative noninvasive means of assessing the functioning of the short-term cardiovascular control systems. We show that sympathetic and parasympathetic nervous activity make frequency-specific contributions to the heart rate power spectrum, and that renin-angiotensin system activity strongly modulates the amplitude of the spectral peak located at 0.04 hertz. Our data therefore provide evidence that the reninangiotensin system plays a significant role in short-term cardiovascular control on the time scale of seconds to minutes.
Energy Technology Data Exchange (ETDEWEB)
Van Engelen, A.; Sehgal, N. [Department of Physics and Astronomy, Stony Brook University, Stony Brook, NY 11794 (United States); Bhattacharya, S. [Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439 (United States); Holder, G. P. [Department of Physics, McGill University, 3600 Rue University, Montreal, Quebec H3A 2T8 (Canada); Zahn, O. [Berkeley Center for Cosmological Physics, Department of Physics, University of California, and Lawrence Berkeley National Labs, Berkeley, CA 94720 (United States); Nagai, D. [Department of Physics, Department of Astronomy and Yale Center for Astronomy and Astrophysics, Yale University, New Haven, CT 06520 (United States)
2014-05-01
The lensing power spectrum from cosmic microwave background (CMB) temperature maps will be measured with unprecedented precision with upcoming experiments, including upgrades to the Atacama Cosmology Telescope and the South Pole Telescope. Achieving significant improvements in cosmological parameter constraints, such as percent level errors on σ{sub 8} and an uncertainty on the total neutrino mass of ∼50 meV, requires percent level measurements of the CMB lensing power. This necessitates tight control of systematic biases. We study several types of biases to the temperature-based lensing reconstruction signal from foreground sources such as radio and infrared galaxies and the thermal Sunyaev-Zel'dovich effect from galaxy clusters. These foregrounds bias the CMB lensing signal due to their non-Gaussian nature. Using simulations as well as some analytical models we find that these sources can substantially impact the measured signal if left untreated. However, these biases can be brought to the percent level if one masks galaxies with fluxes at 150 GHz above 1 mJy and galaxy clusters with masses above M {sub vir} = 10{sup 14} M {sub ☉}. To achieve such percent level bias, we find that only modes up to a maximum multipole of l {sub max} ∼ 2500 should be included in the lensing reconstruction. We also discuss ways to minimize additional bias induced by such aggressive foreground masking by, for example, exploring a two-step masking and in-painting algorithm.
Directory of Open Access Journals (Sweden)
Baudais Jean-Yves
2007-01-01
Full Text Available Bit-loading techniques based on orthogonal frequency division mutiplexing (OFDM are frequently used over wireline channels. In the power line context, channel state information can reasonably be obtained at both transmitter and receiver sides, and adaptive loading can advantageously be carried out. In this paper, we propose to apply loading principles to an spread spectrum OFDM (SS-OFDM waveform which is a multicarrier system using 2D spreading in the time and frequency domains. The presented algorithm handles the subcarriers, spreading codes, bits and energies assignment in order to maximize the data rate and the range of the communication system. The optimization is realized at a target symbol error rate and under spectral mask constraint as usually imposed. The analytical study shows that the merging principle realized by the spreading code improves the rate and the range of the discrete multitone (DMT system in single and multiuser contexts. Simulations have been run over measured power line communication (PLC channel responses and highlight that the proposed system is all the more interesting than the received signal-to-noise ratio (SNR is low.
Angular Power Spectrum and Dilatonic Inflation in Modular-Invariant Supergravity
Hayashi, M J; Okame, Y; Watanabe, T; Hayashi, Mitsuo J.; Hirai, Shiro; Okame, Yusuke; Watanabe, Tomoki
2006-01-01
The angular power spectrum is investigated in the model of supergravity, incorporating the target-space duality and the non-perturbative gaugino condensation in the hidden sector. The inflation and supersymmetry breaking occur at once by the interplay between the dilaton field as inflaton and the condensate gauge-singlet field. The model satisfies the slow-roll condition which solves the \\eta-problem. When the particle rolls down along the minimized trajectory of the potential at a duality invariant fixed point T=1, we can obtain the e-fold value \\sim 57. And then the cosmological parameters obtained from our model well match with the recent WMAP data combined with other experiments. The TT and TE angular power spectra also show that our model is compatible with the data for l > 20. However, the best fit value of \\tau in our model is smaller than that of the \\Lambda CDM model. These results suggest that, among supergravity models of inflation, the modular-invariant supergravity seems to open a hope to constru...
An asymptotically unbiased minimum density power divergence estimator for the Pareto-tail index
DEFF Research Database (Denmark)
Dierckx, Goedele; Goegebeur, Yuri; Guillou, Armelle
2013-01-01
We introduce a robust and asymptotically unbiased estimator for the tail index of Pareto-type distributions. The estimator is obtained by fitting the extended Pareto distribution to the relative excesses over a high threshold with the minimum density power divergence criterion. Consistency...
Song, Xizi; Xu, Yanbin; Dong, Feng
2017-04-01
Electrical resistance tomography (ERT) is a promising measurement technique with important industrial and clinical applications. However, with limited effective measurements, it suffers from poor spatial resolution due to the ill-posedness of the inverse problem. Recently, there has been an increasing research interest in hybrid imaging techniques, utilizing couplings of physical modalities, because these techniques obtain much more effective measurement information and promise high resolution. Ultrasound modulated electrical impedance tomography (UMEIT) is one of the newly developed hybrid imaging techniques, which combines electric and acoustic modalities. A linearized image reconstruction method based on power density is proposed for UMEIT. The interior data, power density distribution, is adopted to reconstruct the conductivity distribution with the proposed image reconstruction method. At the same time, relating the power density change to the change in conductivity, the Jacobian matrix is employed to make the nonlinear problem into a linear one. The analytic formulation of this Jacobian matrix is derived and its effectiveness is also verified. In addition, different excitation patterns are tested and analyzed, and opposite excitation provides the best performance with the proposed method. Also, multiple power density distributions are combined to implement image reconstruction. Finally, image reconstruction is implemented with the linear back-projection (LBP) algorithm. Compared with ERT, with the proposed image reconstruction method, UMEIT can produce reconstructed images with higher quality and better quantitative evaluation results.
An asymptotically unbiased minimum density power divergence estimator for the Pareto-tail index
DEFF Research Database (Denmark)
Dierckx, G.; Goegebeur, Y.; Guillou, A.
2013-01-01
We introduce a robust and asymptotically unbiased estimator for the tail index of Pareto-type distributions. The estimator is obtained by fitting the extended Pareto distribution to the relative excesses over a high threshold with the minimum density power divergence criterion. Consistency and as...... by a small simulation experiment involving both uncontaminated and contaminated samples. (C) 2013 Elsevier Inc. All rights reserved....
Energy Technology Data Exchange (ETDEWEB)
Jardim, P.L.G., E-mail: pedro.lovato@ufrgs.br [Programa de Pós-Graduação em Microeletrônica, Instituto de Física da Universidade Federal do Rio Grande do Sul, CEP. 91501-970 Porto Alegre (Brazil); Horowitz, F. [Programa de Pós-Graduação em Microeletrônica, Instituto de Física da Universidade Federal do Rio Grande do Sul, CEP. 91501-970 Porto Alegre (Brazil); Felde, N.; Schröder, S.; Coriand, L.; Duparré, A. [Fraunhofer Institute for Applied Optics and Precision Engineering, D 07745 Jena (Germany)
2016-05-01
The Wenzel roughness parameter of isotropic Gaussian surfaces is analytically described in terms of the Power Spectral Density function without the smooth surface approximation. This Wenzel roughness parameter — Power Spectral Density link was examined for distinct roughnesses of Aluminum-oxide thin films. The Power Spectral Density functions of the surfaces were determined in a wide spatial frequency range by combining different scan areas of Atomic Force Microscopy measurements. The calculated results presented a good agreement with the Wenzel roughness parameter values obtained directly from the topography measured by Atomic Force Microscopy. Finally, wetting behavior was ascertained through determination of water contact angles, including superhydrophobic behavior. This approach, together with an empirical procedure based on a structural parameter, can predict the wetting properties of a surface by taking all its relevant roughness components into account. - Highlights: • Wenzel roughness parameter and Power Spectral Density are theoretically linked. • The formula is tested for Alumina surfaces with distinct roughnesses. • The formula agrees with the experimental data from Atomic Force Microscopy. • The proper contribution of topography in surface wetting can be ascertained.
The reasons for the high power density of fuel cells fabricated with directly deposited membranes
Vierrath, Severin; Breitwieser, Matthias; Klingele, Matthias; Britton, Benjamin; Holdcroft, Steven; Zengerle, Roland; Thiele, Simon
2016-09-01
In a previous study, we reported that polymer electrolyte fuel cells prepared by direct membrane deposition (DMD) produced power densities in excess of 4 W/cm2. In this study, the underlying origins that give rise to these high power densities are investigated and reported. The membranes of high power, DMD-fabricated fuel cells are relatively thin (12 μm) compared to typical benchmark, commercially available membranes. Electrochemical impedance spectroscopy, at high current densities (2.2 A/cm2) reveals that mass transport resistance was half that of reference, catalyst-coated-membranes (CCM). This is attributed to an improved oxygen supply in the cathode catalyst layer by way of a reduced propensity of flooding, and which is facilitated by an enhancement in the back diffusion of water from cathode to anode through the thin directly deposited membrane. DMD-fabricated membrane-electrode-assemblies possess 50% reduction in ionic resistance (15 mΩcm2) compared to conventional CCMs, with contributions of 9 mΩcm2 for the membrane resistance and 6 mΩcm2 for the contact resistance of the membrane and catalyst layer ionomer. The improved mass transport is responsible for 90% of the increase in power density of the DMD fuel cell, while the reduced ionic resistance accounts for a 10% of the improvement.
Veerman, J.; de Jong, R. M.; Saakes, M.; Metz, S. J.; Harmsen, G. J.
2009-01-01
Reverse electrodialysis (RED) generates electricity through the entropy increase from the mixing of sea and river water. Two important RED process parameters were investigated: power density (in Watts per square meter membrane) and the thermodynamic efficiency Beside this, we quantified losses in a
Power spectral density of the heterogeneous fracture compliance from scattered elastic wavefields
Minato, S.; Ghose, R.
2014-01-01
Using the scattered elastic wavefield, a method to derive the power spectral density (PSD) of the heterogeneous compliance distribution, along the plane of a single fracture, is formulated. The method involves estimation of the stress field at the fracture depth from the scattered wavefield followed